Welcome to PAMU, ISI

Forthcoming Seminars

14.06.2023 (Wednesday),
at 3.00 pm

Seminar room, PAMU
(Kolmogorov Bhavan)

Simultaneous Inference of Cosmology and Population of Binary Neutron Stars from Gravitational-Waves

Speaker: SOUMENDRA KISHORE ROY, SUNY at Stony Brook, USA

Abstract: LIGO-Virgo-Kagra (LVK) Collaboration has detected two confident binary neutron stars up to the third observing run. One of them (GW170817) has an electromagnetic counterpart helping direct estimation of redshift. But most of the expected detections will not have an electromagnetic counterpart, and hence other methods need to be developed to estimate cosmological parameters. In this talk, we will discuss how to estimate redshift from the population distribution of the source frame mass of binary neutron stars. In the first half of the talk, we will deal with a pedagogical set-up to infer both cosmological and population level parameters simultaneously. We will also present a realistic forecast for the current and future observations in LVK. Finally we will end with a remark on the number of events needed to get a sub-percent measurement of the Hubble constant to comment on the existence of Hubble tension.

Past Seminar List

11.05.2023 (Thursday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	LINEAR OPTICS BASED LOCAL DISCRIMINATION OF QUANTUM STATES Speaker: Prof. Sibasish Ghosh, The Institute of Mathematical Sciences, Chennai Abstract: Experimental implementations of linear optics based quantum information processing tasks are of paramount importance due to ease in implementation, although it often suffers from reliability. We need to, therefore, understand properly what is the ultimate efficiency of any linear optics based quantum information processing task, and thereby, to look for minimally resourceful (as well as implementation friendly) non-linear gadgets or, some other minimally resourceful gadgets (e.g., entanglement in other degrees of freedom, etc.) to achieve 100% (or, nearby) efficiency in the respective implementations. Here, in the present talk, we focus on the corresponding scenario in the context of the well-known issue of LOCC (local quantum operations and classical communication) discrimination of bi-partite quantum states -- shared between distant labs. When we are not concerned about any specific physical implementation of LOCC based state discrimination task (i.e., when we look at the problem just mathematically within the purview of quantum theory), we already have several important examples of sets of LOCC- indistinguishable states as well as sets of LOCC- distinguishable states -- using one or more than one copy of the individual states. We will look at some such examples of sets of LOCC-distinguishable states from the perspective of their implementations via linear optics, and thereby, try to figure out the limitations, if any. We will then briefly discuss about how to overcome such limitations using extra resources.
12.04.2023 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Triplet Fermions as the Possible Source of Dark Matter, Neutrino Mass and Baryon Asymmetry of the Universe Speaker: Dr. SARIF KHAN, Goettingen University, Germany Abstract: The motivation of this talk will be to explain three well-accepted standard model (SM) problems namely dark matter (DM), neutrino mass and baryon asymmetry of the Universe (BAU) which need beyond SM physics to be tackled. In this context, I will try to discuss the triplet fermions as a suitable dark matter candidate and the possible origin of the neutrino mass and BAU. First, I will discuss the present bounds on the triplet fermions coming from direct detection, indirect detection and collider search of DM. The bounds reflect that the neutral part of the triplet fermion can not satisfy the full abundance of DM. As a remedy, I elaborate on the possible ways to make it a viable DM candidate. The first approach is by adding a minimal set of particles which will help us to have either a WIMP or FIMP type DM candidate depending on the neutral components mass. An interesting finding of this study will be to probe the FIMP type DM at the proposed MATHUSLA detector. The second approach will discuss another possibility of making it a viable DM with full DM abundance by introducing the non-standard cosmology where we assume the presence of an extra species before BBN whose energy density dominates over the radiation in the early times. With the non-standard cosmology, we will discuss the possible origin of BAU and the change of the leptogenesis scale to the usual standard case which has been studied before. As usual, the triplet fermions which take part in the leptogenesis will generate neutrino mass by the Type III seesaw mechanism.
22.03.2023 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	ALLEVIATING TENSIONS IN COSMOLOGY Speaker: DR. SHREYA BANERJEE, Friedrich Alexander University, Germany Abstract: The Big Bang theory of Cosmology has been the most accurate explanation of cosmic history till date. But it is plagued with some subtle issues which await resolution. I am interested in unravelling the subtleties of the universe at both large and small scales by studying astrophysical objects, phenomena, proven theories and observational data of the universe. I am interested in studying all aspects of the physics of Gravity (General Relativity, Quantum Gravity, Modified Theories of Gravity), Cosmology (Cosmic Microwave Background, Dark Matter, Dark Energy, Inflation, Bounce) and the interrelations between these subjects (for eg. explaining dark matter and dark energy by modified theories of gravity or searching for cosmological signatures of Quantum Gravity theories etc). I am also keen in examining high energy phenomena like Gamma Ray Bursts and Supernovae, both astrophysical and cosmological aspects. In this talk I shall discuss the results of some of my research works that deals with 1) application of modified quantum theory to inflation in order to explain the problem of quantum to classical transition of inflationary perturbations 2) study primordial black holes in the context of bouncing cosmology 3) constraining dark matter condensates 4) gamma ray bursts. In my talk I shall briefly discuss the motivation and interesting outcomes which I have obtained in these research works
20.03.2023 (Monday), at 2.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	A class of Bell diagonal entanglement witnesses in C^4 ⊗ C^4 : optimization and the spanning property Speaker: Dr. ANINDITA BERA, Institute of Physics, Astronomy and Informatics Nicolaus Copernicus University, Poland Abstract: In this talk, I will be discussing two classes of Bell diagonal indecomposable entanglement witnesses in C^4 ⊗ C^4. The first class is a generalization of the well-known Choi witness from C^3 ⊗ C^3 , while the second one contains the reduction map. I will show contrary to C^3 ⊗ C^3 case, the generalized Choi witnesses are no longer optimal. Thereafter, I will talk about an optimization procedure for finding spanning vectors that eventually give rise to optimal witnesses. Operators from the second class turn out to be optimal, however, without the spanning property. I will also discuss the concept of mirrored entanglement witnesses. Our analysis sheds a new light into the intricate structure of optimal entanglement witnesses.
15.03.2023 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	FLAVOR LEPTOGENESIS DURING REHEATING ERA Speaker: Professor ARUNANSU SIL, IIT Guwahati Abstract: We have shown that the process of non-instantaneous reheating during the post-inflationary period can have a sizable impact on the charged lepton equilibration temperature in the early Universe. This suggests a relooking into the flavor effects of leptogenesis where the production and decay of right- handed neutrinos take place within this extended era of reheating. We observe that the decay of the lightest RHN in the set-up not only provides a platform to study flavor leptogenesis during reheating, but also a new paradigm of quasi- thermal leptogenesis emerges.
03.03.2023 (Friday), at 4.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	The 21-cm cosmology Speaker: DR. RAJESH MONDAL, Tel Aviv University, Israel Abstract: Neutral hydrogen (HI) has persisted for much of cosmic history, making it the best tracer to probe the Universe. Observation of the redshifted 21-cm signal due to the hyperfine transition of HI is a promising method to study its three-dimensional distribution in the Universe. The first billion years of cosmic history of the Universe mark the formation of the first stars and galaxies. After years of theoretical predictions, a considerable international effort is now producing the first tentative results, e.g. EDGES, SARAS, GMRT, LOFAR, MWA, HERA, etc. The coming theory and observations will reveal the mysterious era of cosmic dawn and reionization, including the properties of the first stars and galaxies, and possibly more exotic discoveries. There are also plans to probe the pre-stellar "dark ages" with telescopes on the moon. I will give a summary and update on current studies of 21-cm Cosmology and the Epoch of Reionization (EoR).
08.02.2023 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Topological and dynamical aspects of flows in curved fluid membranes Speaker: DR. RICKMOY SAMANTA, Indian Statistical Institute, Kolkata, India Abstract: We will investigate hydrodynamic flows sourced by motors in fluid membranes. The membrane is modelled as a monolayer of viscous fluid, surrounded by external solvents of different viscosities. The in-plane 2D fluid flows sourced by these motors are modelled as point defects, such as vortices and force dipoles. We will explore the effects of membrane curvature and topology on the flows sourced by these motors. We will understand the hydrodynamic interactions between them and discover interesting regimes of co- ordinated activity, vortex lattice formation, global rotation and aggregate formation in the fluid membrane interface. We will also present relevant simulations where several mathematical theorems such as Poincare Index theorem, Liouville-Arnold theorem and Kimura's conjecture will play a role.
07.02.2023 (Tuesday), at 2.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	ELECTROKINETIC TRANSPORT OF COLLOIDAL NANO/MICRO-(BIO)PARTICLES Speaker: DR. PARTHA P. GOPMANDAL, Department of Mathematics, NIT Durgapur Abstract: Colloidal nano/micro-(bio)particles carry an electrostatic charge in aqueous media, and this charge is critical in defining their stability, (bio)adhesion properties, or toxicity toward humans and biota. Determination of interfacial electrostatics of these particles is often performed from zeta potential estimation using the electrophoresis theory by Smoluchowski. The latter, however, strictly applies to the ideal case of hard particles defined by a surface charge distribution under the strict conditions of particle impermeability to electrolyte ions and to flow. Herein, we review sound theoretical alternatives for capturing electrokinetic and therewith electrostatic features of soft colloids of practical interest defined by a 3D distribution of their structural charges and by a finite permeability to ions and/or flow (e.g., bacteria, viruses, nanoplastics, (bio)functionalized particles or engineered nanoparticles). Reasons for the inadequacy of commonly adopted hard particle electrophoresis models when applied to soft particulate materials are motivated, and analytical expressions that properly capture their electrophoretic response are comprehensively reviewed.
27.01.2023 (Friday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Quantum networking with short-range entanglement assistance Speaker: Dr. SIDDHARTHA SANTRA, Assistant Professor, Department of Physics, IIT Bombay, India Abstract: Quantum networks distribute high-fidelity, high-rate entanglement between network nodes as a resource for information processing applications. Current proposals for entanglement distribution in quantum networks utilize the local operation and classical communication (LOCC) framework to obtain high-fidelity states. However, due to the resource intensive nature of LOCC protocols, the entanglement distribution rates over even modest distances (~ 100 km) are extremely low and limit the advantage of all quantum protocols. In this talk, I will describe our recent work that utilizes a previously unused class of entanglement manipulation protocols, the entanglement-assisted local operations and classical communication (ELOCC) protocols, for high-fidelity entanglement distribution in quantum networks. Specifically, I will describe the application of catalytic entanglement transformations over network edges that can significantly enhance the rate of high- fidelity entanglement distribution in quantum networks. I will close with interesting further research directions.
18.01.2023 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	ENTANGLEMENT CATALYSIS FOR QUANTUM STATES AND NOISY CHANNELS Speaker: Dr. CHANDAN DATTA, Centre of New Technologies University of Warsaw, Poland Abstract: Many applications of emerging quantum technologies, such as quantum teleportation and quantum key distribution, require singlets, maximally entangled states of two quantum bits. It is thus of utmost importance to develop optimal procedures for establishing singlets between remote parties. In general, this is not always possible with certainty. However, in some cases, conversion can still be achieved by using a catalyst that remains unchanged in the process. Therefore, it is very important to study the role of catalysis in entangled state transformations. We investigate different aspects of entanglement catalysis, both for quantum states and quantum channels. We prove that entanglement entropy completely characterizes state transformations in the presence of entangled catalysts. Furthermore, for transformations between bipartite pure states, we prove the existence of a universal catalyst, which can enable all possible transformations in this setup. We demonstrate the advantage of catalysis in asymptotic settings, going beyond the typical assumption of independent and identically distributed systems. We further develop methods to estimate the number of singlets that can be established via a noisy quantum channel when assisted by entangled catalysts. For various types of quantum channels, our results lead to optimal protocols, allowing us to establish the maximal number of singlets with a single use of the channel. We also demonstrate the usefulness of catalysis for entanglement distribution via a specific noisy channel.
11.01.2023 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Cosmology with Cosmic Microwave Background and Multi-line Intensity Mapping Speaker: Dr. Anirban Roy, Department of Astronomy, Cornell University, USA Abstract: The observation of the Cosmic Microwave Background (CMB), also known as the first light in the Universe, is a powerful probe to unravel many mysteries of the late-time Universe. During the first half of the talk, I will summarize the recent findings of the different processes in the Universe inferred from the CMB measurements. In the second part of my talk, I will discuss the detailed physics behind the formation of first-generation stars, the evolution of galaxies, and missing baryon problems by considering CMB as a probe of the evolution of baryons and electrons. Furthermore, I will focus on some unsolved problems at the late-time Universe that we aim to solve in a decade. I will also talk about "line intensity mapping" , a novel technique that will provide us with new information from the star formation in galaxies to the expansion of our Universe. I will conclude by describing how these new probes can be useful in resolving the current tension in Cosmology.
04.01.2023 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Light Dirac neutrino portal dark matter with observable \Delta N_{eff} Speaker: Dr. ANIRBAN BISWAS, Center for Quantum SpaceTime (CQUeST) Sogang University, Seoul, South Korea Abstract: We propose a Dirac neutrino portal dark matter scenario by minimally extending the particle content of the Standard Model with three right-handed neutrinos , a Dirac fermion dark matter candidate (ψ) and a complex scalar (φ), all of which are singlets under the SM gauge group. An additional symmetry has been introduced for the stability of dark matter candidate ψ and also ensuring the Dirac nature of light neutrinos at the same time. In this scenario, we can have thermal or non-thermal dark matter depending upon couplings involving these particles. Most importantly, one can easily correlate the cosmological evolution of dark matter with the dynamics of right-handed neutrinos. This leads to a strong constraint on dark matter parameter space from the measurement of the effective number of relativistic degrees of freedom by Planck. The next generation experiments like CMB-S4, SPT-3G etc. will have the required sensitivities to probe a major portion of the entire model parameter space, offering a promising way of probing such light dark matter, where the traditional direct detection experiments are still not sensitive enough.
03.01.2023 (Tuesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	QUANTUM RAYCHAUDHURI EQUATION: IMPLICATIONS FOR SPACETIME SINGULARITIES AND THE QUANTUM ORIGIN OF LAMBDA Speaker: Prof. SAURYA DAS, University of Lethbridge, Canada Abstract: The Raychaudhuri equation predicts the convergence of geodesics and gives rise to the singularity theorems. The quantum Raychaudhuri equation (QRE), on the other hand, shows that quantal trajectories, the quantum equivalent of geodesics, do not converge and are not associated with any singularity theorems. Furthermore, the QRE gives rise to the quantum corrected Friedmann equation. The quantum correction is dependent on the wavefunction of the perfect fluid whose pressure and density enter the Friedmann equation. We show that for a suitable choice of the wavefunction this term can give rise to a small positive cosmological constant, just as observed in nature. We discuss implications.
29.12.2022 (Thursday), at 4.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Self-Similar Gravitational Dynamics, Singularities and Criticality in 2D Speaker: Dr. UPAMANYU MOITRA, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy Abstract: In the talk, I will discuss continuously self- similar gravitational dynamics in 1+1 spacetime dimensions. I will show how the assumption of self-similarity fixes the form of the two-dimensional theory, two classes of which are well-known in the literature. I will discuss some exotic static solutions and how inclusion of matter fields leads to non-trivial dynamics. I will argue for the occurrence of singularities based on a simple feature of differential equations. Time permitting, I will also discuss numerical work relating to dynamics of matter field collapse.
28.12.2022 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	ARBITRARY SEPARATION IN ONE-WAY ZERO-ERROR QUANTUM COMMUNICATION COMPLEXITY OF RELATIONS WITH FINITE SET OF INPUTS Speaker: Dr. SOME SANKAR BHATTACHARYA, ICTQT, University of Gdansk, Poland Abstract: Communication complexity of functions plays a pivotal role in many computation and communication tasks. In this article we consider communication complexity of relations (CCR), where the receiver outputs one of many correct answers. We show that there exists a class of relations such that there is no advantage when the nature of the communication is quantum. However, a stronger version of the task, where the receiver is required to output all correct answers in different runs, entails quantum advantage. We call this task strong communication complexity of relations (S-CCR). Interestingly one of the examples of such a task imply quantum advantage in communication without contextuality. A randomized version of the task unveils curious ordering of communication and shared resources. Besides foundational importance, this work explores a number of applications of S-CCR such as dimension witnesses, detecting nonclassical resources under information constraints and detection of Mutually Unbiased Bases (MUBs).
21.12.2022 (Wednesday), at 11.00 am Seminar room, PAMU (Kolmogorov Bhavan)	One Day Tutorial on Sensitivity Analysis in Dynamic Systems SEAVEA Toolkit Speaker: Dr. Arindam Saha, Brunel University, London Abstract: In this tutorial, we would be providing a general overview of the various tools in the SEAVEA toolkit with detailed hands- on-experience in variance based sensitivity analysis. The participants would be guided to install the tools on their laptops and conduct sensitivity analysis for models which are currently developed in the SEAVEA project. We can also provide guidance on how to integrate any program that the participants have already developed to the SEAVEA toolkit so that sensitivity analysis can be performed on them. With this tutorial we hope to highlight the utility of sensitivity analysis in dynamical models and make it more accessible to a wider audience. Given its applicability, importance and user-friendliness, we also hope that more research groups will find the tools in the SEAVEA toolkit useful in improving their research capabilities.
20.12.2022 (Tuesday), at 4.30 pm NAB-1, Ground Floor (A.N. Kolmogorov Bhavan)	BELL'S THEOREM: REJECTION OF EINSTEIN’S CONCEPT OF LOCAL-REALISM Speaker: Prof. Guruprasad Kar, Physics and Applied Mathematics Unit, Indian Statistical Institute, Kolkata Abstract: The experimental works on which Nobel Prizes have been awarded this year, involve a very important result discovered by John. S. Bell in 1964. This is famously known as Bell's theorem and has been considered to be the ‘most profound discovery of Science’ by some physicists. Bell's theorem shows that quantum world is not compatible with the twin concepts of local-realism propounded by Einstein. Experiments establish that nature is indeed incompatible with local-realism. In this talk we shall discuss the work of John Bell in a simplest possible way. In particular, no expertise in quantum mechanics is needed to understand the essence of Bell's theorem.
14.12.2022 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Uncertainty Relations in Pre- and Post-Selected Systems Speaker: Prof. Sibasish Ghosh, Optics and Quantum Information Group The Institute of Mathematical Sciences C. I. T. Campus, Taramani, Chennai-600113 Abstract: Robertson-Heisenberg like uncertainty relation is derived for two incompatible observables in a pre- and post-selected (PPS) quantum system which can express the impossibility of jointly sharp preparation of pre- and post-selected quantum states for measuring those observables. Motivated by the fact that when the post-selected state is same as the pre-selected state, PPS system turns to be a standard system and we take this as our basis of the derivation for the PPS system based standard deviation (uncertainty). We provide here physical interpretations of the newly defined standard deviation and the uncertainty relation in the PPS system. It is shown that joint sharp preparation of a quantum state for non-commuting observables is possible when the standard system is transformed into a PPS system with certain conditions, an impossible task in standard system. Some applications of uncertainty and uncertainty relation in the PPS system are provided here: (i) Detection of mixedness of the given pre-selection using two different definitions of the PPS system based standard deviation, (ii) stronger uncertainty relation in the standard system using the uncertainty relation in the PPS system, (iii) genuine quantum mechanical uncertainty relation can be found using the first definition of uncertainty when the pre-selection is a mixed state, (iv) state dependent tight uncertainty relation in the standard system, and (v) tight upper bound for the out-of-time-order correlation function.
8.12.2022 (Thursday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Quantum homogenization in non-Markovian collisional model Speaker: Prof. Sibasish Ghosh, Optics and Quantum Information Group The Institute of Mathematical Sciences C. I. T. Campus, Taramani, Chennai-600113 Abstract: Collisional models are a category of microscopic framework designed to study open quantum systems. The framework involves a system sequentially interacting with a bath comprised of identically prepared units. In this regard, quantum homogenization is a process where the system state approaches the identically prepared state of bath unit in the asymptotic limit. Here, we study the homogenization process for qubits in the non- Markovian collisional model framework generated via additional bath-bath interaction. With partial swap operation as both system-bath and bath-bath unitary, we show that homogenization is achieved irrespective of the initial states of the system or bath units. This is reminiscent of the Markovian scenario, where partial swap is the unique operation for a universal quantum homogenizer. On the other hand, we observe that the rate of homogenization is slower than its Markovian counterpart. Interestingly, a different choice of bath-bath unitary speeds up the homogenization process but loses the universality being dependent on the initial states of the bath units. In our process, we found a regime of transition of non-Markovian dynamics to Markovian dynamics (and vice-versa).
09.11.2022 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Memory effects in exact radiative spacetimes in General Relativity and Modified Gravity Speaker: Indranil Chakraborty, IIT Kharagpur Abstract: Abstract: Following recent work [Zhang, Duval, Gibbons and Horvathy (PRD, 2017)], there has been growing interest in understanding memory effects through the study of geodesic motion. One can, in principle, arrive at a class of memory effects (displacement and velocity memory) by solving the geodesic equation or the equation of geodesic deviation. Another route to memory (also termed as B-memory) involves the study of geodesic congruences by utilising the Raychaudhuri equation. In this talk, we will provide an overview of our recent work on such diverse aspects of memory in the context of exact, radiative solutions in General Relativity and modified theories of gravity.
28.10.2022 (Friday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Assembly of colloids into linear chains and studies of their structure and dynamics. Speaker: Dr. BIPUL BISWAS, Department of Physics, University of Massachusetts Amherst, USA Abstract: In this talk, I am going to discuss about the “Assembly of colloids into linear chains and study of their structure and dynamics”. To assemble the colloids into permanent colloidal linear chains, we investigated a novel ice templating methods as well as we exploit the electric and magnetic field. A novel aspect of this work is to render the colloidal chains active, viz. out of equilibrium, by adsorbing catalytic platinum nanoparticles on their surface and by conducting reactions catalyzed by the nanoparticles. I have demonstrated that the diffusion of passive Brownian chains does not depend on chain flexibility whereas the diffusion of “active” colloidal chains is a function of their flexibility. Another novel aspect is to render the colloidal chains thermos-responsive by adhering poly N-isopropyl acrylamide micro-gel particles on the colloidal surface. Rigid chains show a modest decrease in size but exhibit no qualitative change in their shape. Relatively flexible chains form compact structures as they collapse, resulting a large increase in the local monomer number density within the chain. Chains with intermediate flexibility show the formation of helical structures on heating. Finally, I am going to talk about micromotors. Here, we study systematically the translational and rotational dynamics of active particle (Janus particles) clusters. By extracting various parameters like net force, the torques and translational and rotational velocities we aim to find a generic relation between the cluster shape, particle distribution and the resultant dynamical trajectories. We expect our work to provide strategies for the designing active entities with tailored dynamical trajectories.
21.10.2022 (Friday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Mapping the Role of the Magnetic Fields and Episodic Accretion in Star-Formation Speaker: Dr. Indrani Das, University of Western Ontario, Canada Abstract: Molecular clouds are the cradles for star-formation. The stars are formed as a result of the gravitational collapse of compact gas-dust prestellar cloud cores. Magnetic fields are one of the important components in molecular clouds for regulating star-formation. Protostellar disks are formed very quickly after the collapse of a molecular cloud core. The formation and evolution of the disks play a crucial role in the formation of the planetesimals. My work focuses on the fundamental properties of core collapse and the evolution of protostar and a disk via analytic and numerical models, and comparing with observations in order to extract new insights. We investigate the fragmentation scales of gravitational instability of a rotationally supported self-gravitating protostellar disk as well as for the molecular cloud using linear perturbation analysis in the presence of nonideal magnetohydrodynamic (MHD) effects. Nonideal MHD effects result in the diffusion of magnetic flux. We show that the influence of the magnetic field and nonideal MHD on the preferred fragmentation mass for collapse leads to a modified threshold, as opposed to a Jeans mass, that might lead to giant planet formation in the early embedded phase. Our results also indicate that the trend found in the observed lifetime for the prestellar cores and fragmentation mass cannot be explained in a purely hydrodynamic scenario. Furthermore, I will also talk about the episodic mass accretion (therefore episodic luminosity) from a disk to star, which is considered to be one of the most important processes in mass growth of protostar. Our analytic work provides insight into global MHD simulations of protostellar disks that we carry out using the FEOSAD simulation code. Our results using FEOSAD demonstrate the long-term evolution of disks, and especially the episodic nature of accretion, which might explain the origin of observed knots in the molecular jet outflows. All of our studies from various perspectives might fill in many gaps of our knowledge of how the pre-main sequence stars formed over time and consolidate the broad picture of star formation.
18.10.2022 (Tuesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Bell-nonlocal correlations in quantum mechanics: foundation and some applications. Speaker: Dr. Ashutosh Rai, Quantum Information Theory Lab, School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea Abstract: John Bell’s seminal theorem revealed that quantum correlations between space- like separated events contradict any local hidden variable explanation for many such correlations. This work lead to resolution of the Einstein-Podolsky-Rosen paradox which emerged from a belief that at the most fundamental level nature respects local-realism. Subsequent experiments confirmed that quantum correlations indeed violate local-realism. Such Bell nonlocal correlations are considered as a powerful resource which lead to many possible applications in quantum information processing. It also forms a basis to ask further foundational questions like what are the limits of quantum nonlocal correlations and how these limits can be understood better. In this talk, we discuss some foundational as well as application aspect of nonlocal correlations. We will consider the simplest setting for a Bell experiment which constitute two space-like separated parties, each performing one of the two possible measurements with binary outcomes. Then we discuss: (i) the geometry (boundary) of the set of quantum correlations, (ii) applications of these correlations in self-testing quantum devices, and (iii) distillation of weak quantum correlations to strong ones.
14.09.2022 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Thermoelectric and Thermal Transport Properties of Different 2D Materials Speaker: Dr. Suman Chowdhury, Department of Physics, Shiv Nadar University, Gautam Buddha Naga, U.P., India Abstract: After the experimental discovery of two-dimensional (2D) graphene, a new horizon has opened up in the field of condensed matter and material science. The exotic and unconventional properties of graphene have led the scientific community to explore its various intriguing properties. Graphene and graphene like other 2D materials possess tremendous potential to completely alter the modern silicon based electronics industry. In this talk, I would like to explore the thermal and thermoelectric properties of different 2D materials from computational perspective. I will try to demonstrate how different 2D materials can be used for converting waste heat into electricity or how it can be used for thermal management applications.
17.08.2022 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	On a three-dimensional nonlinear model of equatorial ocean dynamics and some insight into particle paths for stratified rotational flows Speaker: Biswajit Basu, Professor, School of Engineering, Trinity College, Dublin, Ireland Abstract: This talk focusses on some investigations into a recently developed non-linear, three-dimensional equatorial model for ocean dynamics. The analysis is based on singular perturbation approach and is facilitated by the introduction of a pseudo-stream function. The development of the model had been motivated by observations and the model is able to capture some essential properties of the flow in the equatorial region. Analysis of velocity field and flow paths indicate that several known and unknown features (which are essentially non-linear and three dimensional such as upwelling/downwelling, cellular flow structures, divergence of flow from the equator and extra-equatorial flows, subsurface ocean ‘bridge’ in the equatorial direction and sharp change in gradient of the flow path) exist and can be simulated by the model. A subsequent detailed global bifurcation analyses of a 2D model incorporating wave-current interaction for stratified rotational flows and numerical results from continuation methods reveal the presence of far more complex particle paths, which may affect the primary production and pelagic spices in addition to the mass, carbon and energy transport.
27.07.2022 (Wednesday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Recent development in deep learning: huge transformers and transfer learning Speaker: Dr. S. K. Venkatesan, Chief Scientist, CQRL Bits LLP, Chennai, Tamil Nadu Abstract: We follow the historical development of deep learning from Markovian models to attention based transformer models and discuss the arrival of huge unsupervised models that will form the starting block of future models.
07.07.2022 (Thursday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Resolving the Singularity by Looking at the Dot and Demonstrating the Undecidability of the Continuum Hypothesis Speaker: Dr. Abhishek Majhi, Physics and Applied Mathematics Unit, Indian Statistical Institute, Kolkata Abstract: Einstein’s theory of general relativity, which Newton’s theory of gravity is a part of, is fraught with the problem of singularity that has been established as a theorem by Hawking and Penrose, the latter being awarded the Nobel Prize in recent years. The crucial hypothesis that forms the basis of both Einstein's and Newton’s theories of gravity is that bodies with unequal magnitudes of mass fall with the same acceleration under the gravity of a source object. Since, the validity of Einstein’s equations is one of the assumptions based on which Hawking and Penrose have proved the theorem, therefore, the above hypothesis is implicitly one of the founding pillars of the singularity theorem. In this work, I demonstrate how one can possibly write a non-singular theory of gravity which manifests that the above mentioned hypothesis is only valid in an approximate sense in the “large distance” scenario. To mention a specific instance, under the gravity of the earth, a 5 kg and a 500 kg fall with accelerations which differ by approximately 113.148*10-32 meter/sec2 and the more massive object falls with less acceleration. Further, I demonstrate why the concept of gravitational field is not definable in the “small distance” regime which automatically justifies why the Einstein’s and Newton’s theories fail to provide any “small distance” analysis. In the course of writing down this theory, I demonstrate why the continuum hypothesis, as spelled out by Goedel, is undecidable. The theory has several aspects which provide the following realizations: (i) Descartes’ self-skepticism concerning exact representation of numbers by drawing lines (ii) Born’s wish of taking into account “natural uncertainty in all observations” while describing “a physical situation” by means of “real numbers” (iii) Klein's vision of having “a fusion of arithmetic and geometry” where “a point is replaced by a small spot” (iv) Goedel's assertion about “non-standard analysis, in some version” being “the analysis of the future”. To further justify Goedel's assertion, I provide a glimpse of what I may call ‘non-standard physics’.
20.06.2022 (Monday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Quantum intersection with applications to hypothesis testing Speaker: Dr. Naqueeb Ahmad Warsi; Electronics and Communication Sciences Unit, Indian Statistical Institute, Kolkata Abstract: In this talk we will discuss the problem of intersection of subspaces in the context of measurement of a quantum state. We will see that this problem is very closely related with Jordan's Decomposition theorem for a pair of projectors. As an application we will discuss the converse of Quantum Stein's lemma which gives the best exponent for the decay of missed detection.
15.06.2022 (Wednesday), at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Unprovability of First Maxwell's Equation in Light of EPR's Completeness Condition Speaker: Dr. Abhishek Majhi, Physics and Applied Mathematics Unit, Indian Statistical Institute, Kolkata Abstract: Maxwell's verbal statement of Coulomb's experimental verification of his hypothesis, concerning force between two electrified bodies, is suggestive of a modification of the respective computable expression on logical grounds. This modification is in tandem with the completeness condition for a physical theory that was stated by Einstein, Podolsky and Rosen in their seminal work. Working with such a modification, I show that the first Maxwell's equation, symbolically identifiable as from the standard literature, is unprovable. This renders Poynting’s theorem to be unprovable as well. Therefore, the explanation of ‘light’ as ‘propagation of electromagnetic energy’ comes into question on theoretical grounds.
01.06.2022 (Wednesday), at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Generalization of Freudenthal Duality for Near-Extremal Black Holes Speaker: Dr. Taniya Mandal Postdoc, School of Physics, University of the Witwatersrand, Johannesburg, South Africa Abstract: Freudenthal duality (F-duality), an anti-involution of charge vectors keep the entropy and attractor solutions invariant for an extremal supersymmetric black hole. This duality holds for both ungauged and gauged extremal black holes in four dimensions. In this talk, I will discuss the effect of F-duality on the entropy of a near-extremal black hole. Specifically, I will consider double-extremal STU black holes in four dimensional, N=2, ungauged supergravity. It is well known that the two-dimensional Jackiw-Teitelboim (JT) gravity governs the dynamics of the near-horizon regions of higher dimensional, near-extremal black holes. Thus, dimensionally reducing the four-dimensional supergravity theory one can construct a JT-gravity like model and compute the near-extremal entropy. I will then analyze the effect of F-duality on this near-extremal entropy. I will show that the F-duality breaks down for the case of near-extremal solutions if one considers the duality operation generated through near-extremal entropy rather than the extremal one.
11.05.2022 (Wednesday), at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Does Quantum Bayes' Rule Affirm Consistency in Measurement Inferences in Quantum Mechanics? Speaker: Dr. Manabendra Nath Bera, Indian Institute of Science Education and Research, Mohali Abstract: Classical Bayes' rule lays the foundation for the classical causal relation between cause (input) and effect (output). This rule is believed to be universally true for all physical processes. On the contrary, we show that it is inadequate to establish correct correspondence between cause and effect in quantum mechanics. In fact, there are instances where the use of classical Bayes' theorem leads to inconsistencies in quantum measurement inferences, such as Frauchiger-Renner's paradox. As a remedy, we introduce a deterministic causal relation based on quantum Bayes' rule. It applies to general quantum processes even when a cause (or effect) is in a coherent superposition with other causes (or effects) as allowed by quantum mechanics and in the cases where causes belonging to one system induce effects in some other system as it happens in quantum measurement processes. This enables us to resolve Frauchiger-Renner's paradox and reaffirm that quantum mechanics can consistently explain its use. We also revisit Hardy's paradox and bipartite non-locality without a Bell-inequality and propose a possible resolution to the inconsistencies using quantum Bayes' rule. We discuss the consequences of our results.
27.04.2022 (Wednesday), at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Primordial Magnetogenesis: An EFT Approach. Speaker: Mr. Abhishek Naskar Postdoctoral Fellow, Indian Institute of Technology, Bombay Abstract: A detectable amount of magnetic field can be probed at all scales of the Universe. There are various possible origins of this observed magnetic field and it is very much possible that this magnetic field is generated during the primordial stage of the Universe. There are various models for the primordial magnetogenesis scenario and if the inflationary background is considered one needs to break conformal symmetry to generate a sufficient amount of magnetic field. To break conformal symmetry one can introduce different couplings between electromagnetic field and inflaton field or add higher derivative terms to the theory. One can also introduce different primordial scenarios like matter bounce to produce sufficient magnetic fields. One interesting way to study these different mechanisms of primordial magnetogenesis is to apply the generic approach of Effective Field Theory (EFT) where the system is described by EFT parameters and different choices of parameters correspond to different models and this approach is successfully applied to study the inflationary perturbations. In this talk, we will try to describe a consistent EFT framework for the primordial magnetogenesis scenario.
04.04.2022 (Monday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	IID and problem specific samples of random quantum states from quantum Wishart distributions. Speaker: Dr. Shrobona Bagchi, Center for Quantum Information, Korea Institute of Science and Technology (KIST), Seoul, Korea Abstract: Random samples of quantum states are an important resource for various tasks in quantum information science, and samples in accordance with a problem-specific distribution can be indispensable ingredients. Some algorithms generate random samples by a lottery that follows certain rules and yield samples from the set of distributions that the lottery can access. Other algorithms, which use random walks in the state space, can be tailored to any distribution, at the price of autocorrelations in the sample and with restrictions to low-dimensional systems in practical implementations. In this work, we present a two-step algorithm for sampling from the quantum state space that overcomes some of these limitations. We first produce a CPU-cheap large proposal sample, of uncorrelated entries, by drawing from the family of complex Wishart distributions, and then reject or accept the entries in the proposal sample such that the accepted sample is strictly in accordance with the target distribution. We establish the explicit form of the induced Wishart distribution for quantum states. This enables us to generate a proposal sample that mimics the target distribution and, therefore, the efficiency of the algorithm, measured by the acceptance rate, can be many orders of magnitude larger than that for a uniform sample as the proposal. We demonstrate that this sampling algorithm is very efficient for one-qubit and two-qubit states, and reasonably efficient for three-qubit states, while it suffers from the “curse of dimensionality” when sampling from structured distributions of four-qubit states.
31.03.2022 (Thursday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Is “0.0=0” true or false?: A dilemma concerning quadratic equation. Speaker: Mr. Ramkumar Radhakrishnan, National Institute of Technology, Surat, India Abstract: Given “ab = 0”, considering the arithmetic truth “0.0 = 0” we conclude that one possibility is “both a = 0 and b = 0”. Consequently, the roots of a quadratic equation appear to be mutually inclusive. However, the situation can be viewed as a ‘decision problem’ (Hilbert- Ackermann). Working with mutual inclusivity of the two roots, by choice, the concerned variable can acquire multiple identities in the same process of reasoning or, at the same time. The law of identity gets violated, which we call the problem of identity. In current practice such a step of reasoning is ignored by choice, resulting in the subsequent denial of “0.0 = 0”. Here, we deal with the problem of identity without making such a choice of ignorance. We demonstrate that the concept “identity of a variable” is meaningful only in a given context and does not have any significance in isolation other than the symbol, that symbolizes the variable, itself. We demonstrate visually how we actually realize multiple identities of a variable at the same time, in practice, in the context of a given quadratic equation. In this work we lay the foundations, based on which we intend to bring forth some hitherto unattended facets of reasoning concerned with the classical harmonic oscillator and the principle of superposition.
14.03.2022 (Monday), at 12.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Understanding multifractal, scale-free and small world weighted planar stochastic lattice. Speaker: Prof. Md. Kamrul Hassan, Theoretical Physics Group, Department of Physics, University of Dhaka, Dhaka 1000, Bangladesh Abstract: In this talk, we will discuss a class of weighted planar stochastic lattice (WPSL1) created by random sequential nucleation of seed from which a crack is grown parallel to one of the sides of the chosen block and ceases to grow upon hitting another crack. It results in the partitioning of the square into contiguous and non-overlapping blocks. Interestingly, we find that the dynamics of WPSL1 is governed by infinitely many conservation laws and each of the conserved quantities, except the trivial conservation of total mass or area, is a multifractal measure. On the other hand, the dual of the lattice is a scale-free network as its degree distribution exhibits a power-law. The network is also a small-world network as we find that (i) the total clustering coefficient C is high and independent of the network size and (ii) the mean geodesic path length grows logarithmically with N. Besides, the clustering coefficient of the nodes which have degree k decreases exactly as 2/(k − 1) revealing that it is also a nested hierarchical network.
11.03.2022 (Friday), at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Universal schemes for detecting entanglement in two-mode Gaussian states: Stokes-like operator based approach. Speaker: Prof. Sibasish Ghosh, Theoretical Physics Group, The Institute of Mathematical Sciences (IMSc), Chennai, India Abstract: Detection of entanglement in quantum states is one of the most important problems in quantum information processing. However, it is one of the most challenging tasks to find a universal scheme which is also desired to be optimal to detect entanglement for all states of a specific class - as always preferred by experimentalist. Although, the topic is well studied, at least in the case of lower dimensional compound systems (e.g., two-qubit systems), but in the case of continuous variable systems, this remains as an open problem. Even in the case of two-mode Gaussian states, the problem is not fully resolved. Here, we try to address this issue. At first, a limited number of Hermitian operators is given to test the necessary and sufficient criterion on the covariance matrix of separable two-mode Gaussian states. Thereafter, we present an interferometric scheme to test the same separability criterion in which the measurements are being done via Stokes-like operators. In such case, we consider only single-copy measurements on a two-mode Gaussian state at a time and the scheme amounts to the full state tomography. Although this latter approach is a linear optics based one, nevertheless it is not an economic scheme. Resource-wise a more economical scheme than the full state tomography can be obtained if we consider measurements on two copies of the two-mode Gaussian state at a time. However, optimality of the scheme is not yet known.
09.03.2022, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Sources of Primordial Gravitational Waves as Probe of Particle Physics. Speaker: Dr. Anish Ghoshal, Institute of Theoretical Physics, University of Warsaw, Poland Abstract: In this talk I describe various primordial sources of Gravitational Waves: inflationary tensor perturbations, primary and secondary, reheating, (p)reheating, phase transitions, cosmic strings, domain walls. I will show how a stochastic background of Gravitational Waves (SBGW) spectrum from such sources of cosmic origin acts as complementary tests of particle physics models compared to other laboratory searches and astrophysical observations.
05.01.2022, at 2.30 pm Seminar room, PAMU (Kolmogorov Bhavan) (Postponed)	Inadequacy of classical logic in basic mathematical science: a self-inquiry concerning quadratic equation, the principle of superposition and the classical harmonic oscillator. Speaker: Dr. Abhishek Majhi. Physics and Applied Mathematics Unit, Indian Statistical Institute, Kolkata Abstract: In the course of the development of modern science, inadequacy of classical logic and Eastern philosophy have generally been associated only with quantum mechanics in particular. Our motive is to showcase a deviation from this prototypical association. In view of this, we discuss the following. Considering the arithmetic truth “0.0 = 0” we discuss that the roots of a quadratic equation are mutually inclusive. Therefore, the concerned variable can acquire multiple identities in ``the same process of reasoning'' (Boole) or, at ``the same time'' (Descartes). The law of identity (Leibniz) gets violated, which we call the problem of identity. In current practice such a step of reasoning is ignored by choice, resulting in the subsequent denial of “0.0 = 0”. Here, we deal with the problem of identity without making such a choice of ignorance. We demonstrate that: (i) the concept “identity of a variable” is meaningful only in a given context and does not have any significance in isolation other than the symbol, that symbolizes the variable, itself; (ii) in current practice, we are indeed in the habit of visually realizing multiple identities of a variable at the same time while graphically analyzing a given quadratic equation; (iii) we indeed implement the mutual inclusiveness of the two roots of a quadratic equation, through intuition, while we write the general solution of a classical harmonic oscillator by applying the principle of superposition. We discuss how the basic principles of classical logic are inadequate to explain our act of writing the general solution of the classical harmonic oscillator. This work, on one hand, provides a glimpse of the Brouwer- Hilbert controversy in the Western literature, albeit in a simple context, and on the other hand, provides a demonstration of the Middle-Way as the foundation of human reasoning as used to be discussed, notably, by the Buddha (also Sanjaya, Nagarjuana) in the Eastern literature.
29.12.2021, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan) (Postponed)	On composition of multipartite quantum systems: perspective from time- like paradigm. Speaker: Dr. Manik Banik. School of Physics, IISER Thiruvananthapuram, Kerala, India. Abstract: Figuring out the physical rationale behind natural selection of quantum theory is one of the most acclaimed quests in quantum foundational research. This pursuit has inspired several axiomatic initiatives to derive mathematical formulation of the theory by identifying general structure of state and effect space of individual systems as well as specifying their composition rules. This generic framework can allow several consistent composition rules for a multipartite system even when state and effect cones of individual subsystems are assumed to be quantum. Nevertheless, for any bipartite system, none of these compositions allows beyond quantum space-like correlations. We will show that such bipartite compositions can admit stronger than quantum correlations in the time-like domain and, hence, indicates pragmatically distinct roles carried out by state and effect cones. We discuss consequences of such correlations in a communication task, which accordingly opens up a possibility to test the actual composition between elementary quanta.
22.12.2021, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	From abstract matrix models to observations in the sky. Speaker: Dr. Suddhasattwa Brahma. Higgs Centre for Theoretical Physics, School of Physics & Astronomy. The University of Edinburgh, Scotland, UK. Abstract: The BFSS matrix model is a proposed non-perturbative definition of M- theory in which space is emergent. In this talk, I shall present a new paradigm of early- universe cosmology in the context of the BFSS theory. Specifically, I will show that matrix theory leads to an emergent non-singular cosmology which, at late times, can be described by an expanding phase of standard Big Bang cosmology. Crucially, the thermal fluctuations in the emergent phase source an approximately scale-invariant spectrum of cosmological perturbations. Hence, this model leads to a successful scenario for the origin of perturbations responsible for the currently observed structure in the universe, while providing a consistent UV-complete description, and naturally overcomes many of the obstacles of the current paradigm of inflation as an effective field theory.
08.12.2021, at 4.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Inflationary magnetogenesis with reheating phase from higher curvature coupling. Speaker: Dr Tanmoy Paul, Chandannagar College, Chandannagar, Hooghly-712136, West Bengal. Abstract: We investigate the generation of magnetic fields from inflation, which occurs via breakdown of the conformal invariance of the electromagnetic field, when coupled with the Ricci scalar and the Gauss-Bonnet invariant. For the case of instantaneous reheating, the resulting strength of the magnetic field at present is too small and violates the observational constraints. However, the problem is solved provided there is a reheating phase with a non-zero e-fold number. During reheating, the energy density of the magnetic field is seen to evolve as a^-6 H^-2 and, after that, as a^-4 up to the present epoch (here ‘a’ is the scale factor and ‘H’ the Hubble parameter). It is found that this reheating phase --characterized by a certain e-fold number, a constant value of the equation of state parameter, and a given reheating temperature- renders the magnetogenesis model compatible with the observational constraints. The model provides, in turn, a viable way of constraining the reheating equation of state parameter, from data analysis of the cosmic microwave background radiation. The Schwinger backreaction has been studied in this regard.
07.10.2021, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Electrophoretic transport of soft particles with hydrophobic/hydrophilic rigid inner core: an overview Speaker: Bharti, Department of Mathematics, NIT Patna. Abstract: In the present article, we have studied extensively the electrophoretic transport phenomenon of spherical soft particles. Electrophoresis is one of the important electrokinetic techniques, which is often used to characterize, and separation of colloids. It is commonly used as a separation technique and often used in the separation of DNA, protein molecules, serum to identify paraproteins, etc. Electrophoretic transport phenomenon is also used to understand the electric properties of several bio particles including virus, bacteria, humic cells and macromolecules and may be used to understand the transport of cargo vessel in treatments of various diseases, e.g., cancer, inflammation, multiple myeloma, rental pathological disorders and macroglobulinemia, etc. Thus, the proper understanding of the electrophoretic transport of soft particles is important to understand the characteristics features of various bio-colloids and macromolecules, which can be viewed as soft particles. In this article, we have first elaborated some of the existing simplified models for electrophoretic transport of soft particles. In addition, we have further extended it for the real situation, considering the effect of pH-dependent charge densities of the inner core and peripheral soft polymeric layer, effect of hydrodynamic slip length of the hydrophobic core surface, etc. In our present study, we have restricted ourselves with the low charge and weak electric field assumptions. We have adopted the linear perturbation analysis to linearize the governing equations for flow field, electrostatic potential, spatial distribution of ionic species, electrochemical potential. The reduced form of the governing equations further integrated to derive the closed form analytic expression for electrophoretic mobility of such a particle. We have further highlighted the effect of pertinent parameters on the neutralization of particle charge due to penetration of counterions across the peripheral soft layer.
27.09.2019, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Controlled Light-Matter Interactions: Implications in quantum information processing Speaker: Debabrata Goswami, IIT Kanpur Abstract: Despite the obvious discrepancies between the quantum mechanical and the classical regimes of computation, there has been an inexorable push to establish quantum computation as the dominant methodology for the future. The drive towards miniaturization coupled with the possibility of hitherto unfeasible parallelism overpowers the ugly circuit implementation aspects inherent at quantum scales. Though quantitatively indistinguishable from a classical Turing machine, Quantum computers do not function along with the same operating principles as their classical counterparts. Indeed, analogies to classical computations are limited by the fact that very few algorithms truly show 'quantum supremacy'. Some of the most difficult aspects of quantum computations are the understanding and reinterpretation of classical terms such as computational power, memory, and intelligence in the quantum domain. One of the more elegant implementations of quantum computing and information relies heavily on optical approaches, at the forefront of which, due scalability and near room temperature operation, our techniques excel. These approaches primarily rely on light-matter interactions, typically at ultrashort timescales. Though not directly realizable, ultrashort times can also be connected to the ultra-small sizes. Spatiotemporal control aspects of pulsed laser experiments rely on the ability to modulate the shape of the generated pulses in an efficient manner. Drawing from current state-of-the-art theoretical aspects of computational simulations to reduce the sim-to-real bottlenecks, we devised a novel schematic for the generation of on-the-fly calibrated pulse trains with more accountability than existing techniques under the domain of optimal control theory. The techniques presented today further diminish the divide between experiment and theory.
20.09.2019, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Application of dynamical system technique in f(R) cosmology Speaker: Saikat Chakraborty, IIT Kanpur Abstract: Since any relativistic theory of gravity essentially gives rise to a nonlinear dynamics, import of dynamical systems approach to study gravitational systems, especially cosmology, in general relativity or modified gravity, has a history of quite a few decades as of now. Most of such works deals with homogeneous and isotropic FLRW cosmology as relevant at large scale of the universe, and uses 'expansion normalized' dimensionless dynamical variables. However, nothing prevents the very early universe, either in inflationary or in nonsingular bouncing paradigm, to be slightly anisotropic or inhomogeneous, as long as one prescribes a homogenization or isotropic mechanism within the paradigm. My talk will be based on two of my works (1805.03237 & 1812.01694), which attempts to extend the dynamical systems formulation of f(R) cosmology to homogeneous and anisotropic Bianchi-I spacetime. The first of these works employs the usual expansion normalized dimensionless dynamical variables to construct a phase space and extracts some important results regarding f(R) cosmology, an example being the attractor nature of Starobinski solution. The second work presents an alternative dynamical system formulation and for the first time addresses the issue of the dynamical equivalence of conformally related descriptions of f(R) gravity from the phase space point of view.
19.07.2019, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Incoherent Operations: structure and applications Speaker: Swapan Rana, University of Warsaw, Poland Abstract: The recently introduced resource theory of coherence is modeled with the incoherent operations. In this seminar I shall talk about the structure of (strictly) incoherent operations, namely their Kraus decomposition. Various bounds on the number of Kraus operators will be given, which in general, may not be optimal. However, for the qubit (strictly) incoherent channels, I shall present the optimal decomposition. Importance of this optimal decomposition (e.g. to quantum thermodynamics) will also be mentioned.
04.07.2019, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Scales and gravitation Speaker: Abhishek Majhi, ISI Kolkata Abstract: The notion of 'point', as defined by Euclid, founds the basis of geometry, whether flat or curved. On the other hand, Euclid's analysis of numbers is based on the definition of 'unit' or 'scale' that symbolizes the existence of an object according to human realization. I venture to explore the scenario where one begins with 'scale' instead of 'point'. This simple change in the mindset, in the context of gravitation, leads to some interesting results such as gravitational effect of a test mass itself, regime of validity of universality of free fall, the relation between realization of the existence of test mass to the continuity of the field, etc. On general grounds, the analysis shows the connection among arithmetic, calculus and geometry based on how one adjusts resolution or measuring scale.
28.05.2019, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Open quantum theory of two entangled atoms in De Sitter Universe Speaker: Sayantan Choudhury, Max Planck Institute for Gravitational Physics (AEI), Potsdam, Germany Abstract: In this paper, our prime objective is to connect the curvature of our observable De Sitter Universe with the spectroscopic study of entanglement of two atoms in an open quantum system (OQS). The OQS considered in our work is made up of two atoms which are represented by Pauli spin tensor operators projected along any arbitrary direction. They mimic the role of a pair of freely falling Unruh De-Witt detectors, which are allowed to non-adiabatically interact with a conformally coupled massless probe scalar field in the De Sitter background. The effective dynamics of the atomic detectors are actually an outcome of their non-adiabatic interaction, which is commonly known as the Resonant Casimir Polder Interaction (RCPI) with the thermal bath. We find from our analysis that the RCPI of two stable entangled atoms in the quantum vacuum states in OQS depends on the De Sitter space-time curvature relevant to the temperature of the thermal bath felt by the static observer. We also find that, in OQS, RCPI produces a new significant contribution appearing in the effective Hamiltonian of the total system and thermal bath under consideration. This will finally give rise to Lamb Spectroscopic Shift, as appearing in the context of atomic and molecular physics. This analysis actually plays a pivotal role to make the bridge between the geometry of our observed Universe to the entanglement in OQS through Lamb Shift atomic spectroscopy. In two atomic OQS, Lamb Shift spectra are characterised by a $L^{−2}$ decreasing inverse square power law behaviour when inter atomic Euclidean distance (L) is much larger than a characteristic length scale (k) associated with the system, which quantifies the breakdown of a local inertial description within OQS. On the other hand, the RCPI of this two atomic OQS immersed in a thermal bath in the background of Minkowski flat Universe is completely characterised by a temperature independent $L^{−1}$ decreasing inverse power law. This mimics exactly the same situation where the characteristic length scale k is sufficiently large compared to the interatomic Euclidean distance between the two atoms. Thus, we are strongly aiming to connect the curvature of the background space-time of our Universe to open quantum Lamb Shift spectroscopy by measuring the quantum properties of a two entangled OQS in the atomic experiment.
29.05.2019, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Age-structured and delay differential-difference model of hematopoietic stem cell dynamics Speaker: Mostafa Adimy, INRIA Lyon France Abstract: We investigate a mathematical model of hematopoietic stem cell dynamics. We take two cell populations into account, quiescent and proliferating one, and we make the difference between dividing cells that enter directly to the quiescent phase and dividing cells that return to the proliferating phase to divide again. The resulting model is a system of two age-structured partial differential equations. By integrating this system over the age, we reduce it to a delay differential-difference system. We investigate the stability analysis of the unique positive steady state, the most biologically meaningful one, and the existence of a Hopf bifurcation. This allows to determine the stability area, which is related to a delay-dependent characteristic equation. Numerical simulations illustrate our results on the asymptotic behaviour of the steady states and show very rich dynamics of this model. This study may be helpful in understanding the uncontrolled proliferation of blood cells in some diseases, in particular the existence of periodic oscillations observed in patients with some cyclical hematological disorders.
10.05.2019, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Portrait of a Dark Face Speaker: Tapas K Das, HRI, Allahabad Abstract: In this colloquium, I shall talk about the very recent discovery that shook the scientific community: Image of the region extremely close to the horizon of the central black hole of M87 has been has been mapped using an array of radio telescopes spread across the globe. Astronomy community is considering this one to be one of the greatest discoveries (observational) in astrophysics/general relativity. The talk will be presented in such a way (without absolutely any mathematics) so that the content can be well understood to a general audience with basic science background. The massive black hole at the heart of the Milky way Galaxy possesses the largest apparent angular size of the event horizon. On the other hand, the super-masive black hole at the dynamical centre of the active galaxy M87 is known to have the second largest angular size of the event horizon. Such information tempted the astronomers to introduce a novel observational technique to resolve the length scale comparable to the size of the event horizon of our Galactic centre black hole, as well as of the central black hole of M87, and to directly image the event horizon using radio waves. Recently, image of the region extremely close to the horizon of the central black hole of M87 has been has been mapped using an array of radio telescopes spread across the globe (the Event Horizon Telescope), the findings have officially been published through press release worldwide on 10th of April 2019. This path-breaking work will surely help to have deep understanding of the black hole space time, and of strong gravity regions in the universe in general.
01.05.2019, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Higher Curvature correction in Einstein Hilbert Action and Gravitational Collapse Speaker: Soumya Chakrabarti, IIT Kharagpur Abstract: This discussion will be on collapsing spherical stars in theories of gravity carrying higher curvature corrections. While pure General Relativity predicts a straightaway choice between a Black Hole or a Naked Singularity, higher curvature modifications may provide alternative options to emerge as an end state of an imploding mass. Exact solutions in this regard will be discussed as simple examples for (a) an f(R) collapse model and a (b) Scalar-Gauss-Bonnet Collapse.
26.03.2019, at 4.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Impossible Process of Noninteracting Identical Particles Speaker: Aravinda S, PAMU, Indian Statistical Institute Abstract: In the framework of Generalized probabilistic theories (GPT), we illustrate a class of statistical processes in case of two noninteracting identical particles in two modes that satisfies a well motivated notion of physicality conditions namely the double stochasticity and the no-interaction condition proposed by Karczewski et al (Phys. Rev. Lett. 120, 080401 (2018)), which cannot be realized through a quantum mechanical process. This class of statistical process is ruled out by an additional requirement called the evolution condition imposed on two particle evolution. We also show that any statistical process of two noninteracting identical particles in two modes that satisfies all of the three physicality conditions can be realized within quantum mechanics using the beam splitter operation.
26.03.2019, at 2.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Geometry of the quantum set on no-signaling faces Speaker: Ashutosh Rai, International Institute of Physics, Federal University of Rio Grande do Norte, Brazil Abstract: Since Bell's theorem we know that quantum mechanics is incompatible with local hidden variable models, the phenomenon known as quantum nonlocality. However, in spite of steady progress over years, the precise characterization of the set of quantum correlations has remained an elusive quest. There are correlations compatible with the no-signaling principle and still beyond what can be achieved within quantum theory, what has motivated the search for physical principles and computational methods to decide the quantum or post-quantum behavior of correlations. Here we identify a yet new feature of Bell correlations that we call quantum voids: faces of the no-signaling set where all nonlocal correlations are postquantum. Considering the simplest possible Bell scenario we give a full characterization of quantum voids, also understanding its connections to known principles and its potential use as a dimension witness.
11.03.2019, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Constraining Non-thermal Dark Matter by CMB Speaker: Koushik Dutta, SINP Abstract: A period of early matter domination can give rise to the correct dark matter abundance for a broad range of dark matter annihilation rate. We examine this scenario for situations where the annihilation rate is below the nominal value for thermal dark matter 3 × 10^(−26) cm^3 s^(−1) as possibly indicated by some recent experiments. We show that obtaining the correct relic abundance sets a lower bound on the duration of early matter domination era in this case. On the other hand, provided that the post-inflationary universe has an equation of state characterized by w ≤ 1/3, the requirement that the scalar spectral index n_s be within the observationally allowed range limits the duration of this epoch from above. By combining these considerations, we show that the current and future cosmic microwave background experiments can tightly constrain the parameter space for this scenario. In particular, models of inflation with a tensor-to-scalar ratio r below 0.01 may disfavor non-thermal supersymmetric dark matter from a modulus-driven early matter domination epoch.
20.02.2019, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Log-normal Simulations in Redshift Space Speaker: Aniket Agrawal, Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan Abstract: Galaxies in the universe are observed to follow a log-normal distribution. Motivated by this, in this talk I will present a code to generate log-normal galaxy distributions in the universe quickly. The clustering properties of these mocks can be fully predicted analytically in real space. Using linear velocities we are also able to reproduce the large scale redshift space distribution of galaxies. These catalogs are useful for performing end to end tests of analysis pipelines and for Fisher matrix forecasts for future surveys. I will discuss these results and the short comings of this approach.
14.01.2019, at 2.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	The operator theoretic approach to dynamical systems Speaker: Suddhasattwa Das, New York University Abstract: The operator theoretic framework for dynamical systems studies the dynamics induced on some functional space like $C^0(M)$ or $L^2(\mu)$, instead of the trajectories on the underlying phase space $M$. It transforms the dynamics under any nonlinear flow $\Phi^t$ into a linear map on some Banach / Hilbert space. The dynamics is induced by the Koopman operator $U^t$, which acts on functions by time shifts, namely, $(U^t f)(x) = f (\Phi^t x)$. The operator theoretic framework offers an alternative way of restating several questions in dynamics, and the spectral properties of $U^t$ have important implications on the actual dynamics. I will discuss the connections of $U^t$ with the statistical / ergodic properties of the underlying dynamics. I will also discuss how these operators can be well approximated by matrices, and discuss various convergence results.
24.12.2018, at 2.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Computational Methods to Identify Driver and Druggable Mutations in Cancer Speaker: Sohini Sengupta, Washington University School of Medicine Abstract: Recently, there has been an enormous corpus of cancer sequencing data through large-scale projects such as The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC). TCGA provides whole genome and exome sequencing data of tumor and matched normal samples for various cancer types. ICGC also studies genomic alterations in tumors across 50 cancer types. These projects provide an unprecedented opportunity for comprehensive discovery of cancer mutations genome-wide. There is an urgent need to systematically reveal the functional implications and oncogenic potentials of genetic mutations recently identified in these large-scale studies. The majority of mutations in cancer samples are incidental passengers; distinguishing between driver and passenger somatic mutations to pinpoint the exact genetic alterations leading to tumor initiation and/or progression still present significant challenges. To meet these challenges, various computational approaches have been developed as effective filters, pruning most of the somatic mutations to a shortlist of high-priority, functional candidates for experimental validation. However, these approaches rely heavily on primary protein sequence context and frequency/mutation rate. Rare driver mutations not found in many cancer patients may be missed with these traditional approaches. Additionally, the structural context of mutations on 3D protein structures is not taken into account and may play a more prominent role in determining phenotype and function. We have created a suite of computational methods to address this gap in knowledge and explore mutations in the context of protein structure and their potential implications in oncogenesis. The oncogenic potentials of the predicted driver mutations can then be confirmed experimentally if the mutation leads either to DNA repair deficiency, cell proliferation, or immune evasion. Discerning drivers from passengers will result in a greater understanding of the mechanisms governing cancer biology and will also have therapeutic implications.
17.12.2018, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Non Gaussian yet Brownian diffusion in Soft Matter Speaker: Suman Dutta, Institute of Mathematical Sciences, Chennai Abstract: Much celebrated Einstein's theory of diffusion considers extreme separation of timescales between solute and solvent particle in a chemical dispersion. Thus, the Fickian diffusion is widely successful in explaining most of the molecular transport which is realized in terms of Gaussian probability distributions of particle displacements. But the local environmental fluctuation in many complex systems dominates the microscopic motion, leading to an intermittence in dynamics, resulting in non-Gaussian displacement distribution where microscopic motion could be explained in terms of a diffusion spectrum, instead of a single diffusion coefficient as in normal Brownian motion. Our investigation in a generic driven system show notions of 'Non-Gaussian yet Brownian' motion which I shall motivate further.
22.11.2018, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Dynamical synchronization transition in interacting electron systems Speaker: Tanay Nag, MPIPKS, Dresden Germany Abstract: Using graphene irradiated by an intense bi-circular pulse laser as a prototypical example, we theoretically investigate how to selectively generate coherent oscillation of electronic orders such as charge density waves (CDW), where the key is to use tailored fields that match the crystalline symmetry broken by the target order. After the pump, a macroscopic number of electrons start oscillating and coherence is built up through a dynamical synchronization transition described by an effective Kuramoto model. The oscillation is detectable as a coherent light emission at the synchronized frequency and may be used as a purely electronic way of realizing a Floquet state respecting space time crystalline symmetries. In the process, we explore possible flipping of existing static CDW order and generation of higher harmonics. The analysis is done within the time dependent mean field treatment of the extended Hubbard model on the honeycomb lattice.
23.10.2018, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Magntotransport properties of 2D material with tilted Dirac cones Speaker: Firoz Islam, Institute of Physics, Bhubaneswar Abstract: Polymorph of 8-Pmmn borophene exhibits anisotropic tilted Dirac cones. In this talk, I will discuss the consequences of the tilted Dirac cones in magnetotransport properties of 2D sheet of borophene in presence and absence of weak modulation. I will mostly emphasize how to generate valley polarized transport by exploiting opposite tilting of the Dirac cones at two valleys. Finally, if time permit, I will try to cover few more topics like- electron-hole conversion phenomena (Andreev reflection) in thin topological insulator, Cooper pair splitting in a graphene based beam splitter geometry and driven conductance in semi-Dirac material.
26.09.2018, at 2.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Exclusivity principle and unphysicality of the Garg-Mermin correlation Speaker: Aravinda, IMSc Chennai (via skype) Abstract: The question concerning the physical realizability of a probability distribution is quite important in quantum foundations. Recent studies emphasized a principle which was first indicated by Specker. This principle, called Specker's principle, bounds physically realizable correlations. We study Specker's observation in the scenario that involves three inputs each with two outputs. Then using only linear constraints imposed on joint probabilities by this principle, we reveal the unphysical nature of Garg-Mermin (GM) correlation. Interestingly, GM correlation was proposed to falsify the following suggestion by Fine: if the inequalities of Clauser and Horne (CH) holds, then there exists a deterministic local hidden-variable model for a spin-1/2 correlation experiment of the Einstein-Podolsky-Rosen type, even when more than two observables are involved on each side. Our result establishes that, unlike in the CH scenario, the local orthogonality principle at single copy level is not equivalent to the no-signaling condition in the GM scenario.
26.09.2018, at 3.20 pm Seminar room, PAMU (Kolmogorov Bhavan)	Fluctuation-Dissipation in de Sitter Universe Speaker: Ashmita Das, IIT Guwahati (via skype) Abstract: It is well known that a comoving observer/detector in FLRW (FriedmannLemaitre-Robertson-Walker) Universe detects particle radiation in the conformal vacuum (conformal to Minkowski spacetime). A particular well-known example of this is a comoving detector in de Sitter spacetime which percieves thermal radiation even from the conformal vacuum. In this work we address the question that what would be the behaviour of these produced particles from the perspective of a comoving observer in de Sitter spacetime? We calculate the correlation function of the random force due to the particle radiation as measured by the comoving detector and obtain that, it follows fluctuationdissipation theorem. This indicates that the radiated particles exhibit Brownian like motion in this thermal bath.
26.09.2018, at 4.10 pm Seminar room, PAMU (Kolmogorov Bhavan)	Exploring New Vistas in Cosmology Speaker: Satadru Bag, IUCAA Pune (via skype) Abstract: The past two decades have witnessed a tremendous growth in our understanding of cosmology. This understanding has come about because of detailed theoretical modelling on the one hand and cutting-edge observations on the other. Despite the rapid advance in observational techniques there still remain several aspects of theoretical cosmology which are not fully understood. These open questions pertain to the initial big-bang singularity, the present epoch of accelerated expansion and the epoch of the cosmological reionization of hydrogen. However one hopes that upcoming state-of-the-art surveys, well complemented by the recent progress in simulations, will allow one to answer at least some of these open questions in the near future. My doctoral research is focused on revisiting several important open questions in cosmology from new theoretical points of view. In particular, the thesis sheds light on (i) alternatives to the initial big-bang singularity, (ii) properties of dark energy beyond the concordance model (LCDM), (iii) the reionization process in which neutral hydrogen in the intergalactic medium was ionized from the first light sources during redshift 6-20. Focusing on the last two topics, in this talk, I will discuss braneworld models of dark energy and probing reionization using Minkowski functionals and Shapefinders.
25.09.2018, at 2.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Extreme events: Dynamical origins and Predictability Speaker: Arindam Mishra, Jadavpur University Abstract: Extreme events such as rogue waves, tsunamis, earthquakes, share market crashes, can occur spontaneously in nature and have huge adverse consequences. Because of their devastating impact to human life and economy, quantification, prediction and mitigation of extreme events are highly desirable. In many situations, the evolution of natural, engineering, and social phenomena can be represented by mathematical models able to incorporate how the properties of the system change in time. In the same way, we study extreme events from the dynamical system’s point of view. My presentation will be divided in three parts. Firstly, I will talk about some general aspects of extreme events. Next I will talk about our recent work where we have found two routes of extreme events, namely, quasiperiodic and intermittency, in coupled bursting neurons. We considered two Hindmarsh-Rose neurons interacting through chemical synaptic coupling. Quasiperiodic and intermittent routes to extreme events are observed for purely inhibitory and excitatory coupling respectively. The probability distribution of events shows dragon-king like behavior where large events are outliers to a power law. In the last section of my presentation I will discuss my future research plans. In future research I will focus on the quasiperiodic route and on the prediction of extreme events. In case of prediction we will try to define measurable observables that contain early warning signs of upcoming extreme events. When extreme event occurs, the signal becomes chaotic and the sensitivity to initial conditions leads to an inherent uncertainty in chaotic systems even when the system model is deterministic. As a result some uncertainties appear in the prediction and we want to quantify this.
25.09.2018, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Warm Inflation: A better realisation of the accelerated expansion of the nascent Universe? Speaker: Mayukh Raj Gangopadhyay, SINP Kolkata Abstract: Cosmological observations are in very good agreement with an universe that is expanding, spatially flat, homogeneous and isotropic on large scales where the large scale structure originated from primordial perturbations with a nearly gaussian and scale-invariant spectrum. On the theoretical side, the paradigm of slow-roll inflation, a period of accelerated expansion in the early history of the universe, predicts such a primordial spectrum starting with the fluctuations of the inflaton field. In general there are two realisation of the inflationary dynamics: cold inflation and warm inflation. In this talk, I will explain this two dynamical realisations of inflation. The constraints from the observations by Planck satellite has ruled out most of the so called ‘text book’ cold inflation potentials such as quartic potential. I will explain even a quartic potential in warm inflationary paradigm can survive the tight constraints from observations. Finally, I would try to explore the future course of research in the field of inflation and alternative scenarios to inflation.
11.09.2018, at 2.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Black hole entropy from the first principles revisited Speaker: Abhishek Majhi, UNAM, Mexico Abstract: Perhaps one of the most intriguing features of Einstein's theory of general relativity is the prediction of black holes, which can only grow or remain in equilibrium. However, if we quantize matter, then the theory predicts that a black hole emits thermal radiation and behaves like a thermodynamic system possessing an entropy given by one fourth of its area in Planck units ). This fact necessitates the need of a quantum theory of black hole providing the description of microstates that can lead to a derivation of the entropy from the first principles. One such theory, providing the description for microstates of black holes, is Loop Quantum Gravity (LQG). In LQG, one quantizes general relativity in the canonical approach. Unfortunately, the derivation of the entropy in the LQG framework is plagued with a fine tuning problem of a free parameter of the theory. I shall discuss about a possible way to tackle this problem by introducing a new definition of entropy.
07.09.2018, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Bounds on Sum of Neutrino Masses in Various Cosmological Scenarios Speaker: Shouvik Roychoudhury, HRI, Allahabad Abstract: We present strong bounds on the sum of three active neutrino masses ($\sum m_{\nu}$) using selected cosmological datasets and priors in various cosmological models. We use the following baseline datasets: Cosmic Microwave Background (CMB) temperature data from Planck 2015, Baryon Acoustic Oscillations measurements from SDSS-III BOSS DR12, the newly released Type Ia supernovae (SNe Ia) dataset from Pantheon Sample, and a prior on the optical depth to reionization from 2016 Planck Intermediate results. We constrain cosmological parameters with these datasets with a Bayesian analysis in the background of $\Lambda CDM$ model with 3 massive active neutrinos. For this minimal $\Lambda CDM+\sum m_{\nu}$ model we find a upper bound of $\sum m_{\nu} <$ 0.152 eV at 95$\%$ C.L. Adding the high-$l$ polarization data from Planck strengthens this bound to $\sum m_{\nu} <$ 0.118 eV, which is very close to the minimum required mass of $\sum m_{\nu} \simeq$ 0.1 eV for inverted hierarchy. This bound is reduced to $\sum m_{\nu} <$ 0.110 eV when we also vary r, the tensor to scalar ratio ($\Lambda CDM+r+\sum m_{\nu}$ model), and add an additional dataset, BK14, the latest data released from the Bicep-Keck collaboration (which we add only when $r$ is varied). This bound is further reduced to $\sum m_{\nu} <$ 0.101 eV in a cosmology with non-phantom dynamical dark energy ($w_0 w_a CDM+\sum m_{\nu}$ model with $w(z)\geq -1$ for all $z$). Considering the $w_0 w_a CDM+r+\sum m_{\nu}$ model and adding the BK14 data again, the bound can be even further reduced to $\sum m_{\nu} <$ 0.093 eV. For the $w_0 w_a CDM+\sum m_{\nu}$ model without any constraint on $w(z)$, the bounds however relax to $\sum m_{\nu} <$ 0.276 eV. Adding a prior on the Hubble constant ($H_0 = 73.24\pm 1.74$ km/sec/Mpc) from Hubble Space Telescope (HST), the above mentioned bounds further improve to $\sum m_{\nu} <$ 0.117 eV, 0.091 eV, 0.085 eV, 0.082 eV, 0.078 eV and 0.247 eV respectively. This substantial improvement is mostly driven by a more than 3$\sigma$ tension between Planck 2015 and HST measurements of $H_0$ and should be taken cautiously.
21.08.2018, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Genuinely entangled subspace made of all-partition distillable bipartite entanglement Speaker: Sristy Agrawal, IISER Kolkata Abstract: In a multipartite scenario quantum entanglement manifests its most dramatic form when the system state is not a statistical mixture of bipartite factorized density matrices, i.e., genuinely entangled. Subspace of a multipartite Hilbert space, consists of such states only, is called genuinely entangled subspace (GES). A GES is of significant operational interest if it is bidistillable -- all the states supported on it contain free (distillable) entanglement across all bipartitions. In this work we introduce the notion of unextendible biseparable bases (UBB) that provides a adequate method to construct GES. We construct two types -- symmetric and asymmetric -- of such UBBs for every 3-qudit quantum system, with d greater than or equals to 3. Interestingly, we further show that, the symmetric construction leads to a bidistillable-GES. In a complete contrast, we also provide example of genuinely entangled states whose entanglement remain in bound form across every bipartition.
17.08.2018, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Effects of adiabatic index on transonic solution of low angular momentum accretion flow Speaker: Ishika Palit, Center for Theoretical Physics PAS, Poland Abstract: Study of standing and oscillating shocks in accretion flows has become very important since it is recognized that the spectral states of black holes as well as Quasi-Periodic Oscillations (QPOs) observed in light curves of black hole candidates are directly related to the radiative transfer properties of a compact Comptonizing region close to a black hole. More recently, the shock existence was found for the disc-like structure in hydrostatic equilibrium with low angular momentum both in pseudo-Newtonian potential and in full relativistic approach . Thus shocks play a significant role in governing the overall dynamical and radiative processes taking place in accreting matter. I will present the study of gamma dependence of shock waves of slightly rotating accretion flows onto black holes for a more accurate explanation for QPOs observed in light curves of black hole.
06.08.2018, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Non-classical space-time in (loop) quantum gravity Speaker: Suddhasattwa Brahma, APCTP Korea Abstract: General relativity typically predicts singularities when applied to high curvature regimes such as the very early universe or within the cores of black-holes. Therefore, quantum gravity becomes essential in describing the physics of such regions. In particular, loop quantum gravity, when applied to such scenarios, leads to singularity-resolution due to nontrivial quantum corrections resulting in the emergence of modified dynamics near Planck scales. However, a quantum theory of gravity must also describe a theory of quantum space-time. In this talk, I shall focus on the emergence of non-Riemannian space-time due to loop quantum gravity corrections, the main physical consequence of which is dynamical 'signature-change'. Similarities with other approaches such as the Hartle-Hawking proposal shall also be briefly discussed.
07.08.2018, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Astrophysical neutrinos, PeV events at IceCube, and the Direct Detection of Dark Matter Speaker: Dr. Aritra Gupta, TIFR Abstract: In this talk, we discuss the implications of the premise that any new, relativistic, highly energetic neutral particle that interacts with quarks and gluons would create cascade-like events in the IceCube (IC) detector which would be observationally indistinguishable from neutral current deep-inelastic (DIS) scattering events due to neutrinos. Consequently, one reason for deviations, breaks or excesses in the expected astrophysical power-law neutrino spectrum could be the flux of such a particle. Motivated by features in the recent 1347-day IceCube high energy starting event (HESE) data, we focus on particular boosted dark matter (χ) related realizations of this premise, where χ is assumed to be much lighter than, and the result of, the slow decay of a massive scalar (φ ) which constitutes a major fraction of the Universe's dark matter (DM). We show that this hypothesis, coupled with a standard power-law astrophysical neutrino flux is capable of providing very good fits to the present data, along with a possible explanation of other features in the HESE sample: ie, a) the paucity of events beyond ~ 2 PeV b) a spectral feature resembling a dip in the 400 TeV - 1 PeV region and c) an excess in the 50-100 TeV region. We also consider constraints from diffuse gamma ray backgrounds and find that it is indeed very restrictive.
28.02.2018, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Dark Photon Searches and Bounds: Resonant Production in Beam Dump for 8Be anomaly Speaker: Anish Ghoshal, Universit`a di Roma Tre and INFN, Italy Abstract: Search for dark photon and axion-like particles will be described and present bounds on them will be shown. Such a candidate if responsible for 8Be anomaly in the ATOMKI experiment can be produced in PADME experiment in LNF-INFN. Sensitivity and parameter space concerned to this will be discussed.
15.02.2018, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Exotic pairs of stellar undeads: binary radio pulsars with compact companions Speaker: Manjari Bagchi, IMSc Chennai Abstract: Binary radio pulsars with white-dwarfs or other neutron stars or black holes as companions serve as excellent laboratories to test various aspects of basic physics. In this talk, I will explain how orbital and stellar properties (classical and general relativistic) of pulsars, can be probed by timing stable pulsars for long enough time. I will emphasize the prospects of putting more stringent constraints on alternative theories of gravity with the help of pulsar - black hole binaries (to be discovered). I will also discuss the prospect of constraining dense matter equation of state by timing neutron star-neutron star binaries. Finally, I will give a brief update on Indian efforts to detect nano-Hz gravitational waves by timing an ensemble of stable pulsars.
07.12.2017, at 4.15 pm Seminar room, PAMU (Kolmogorov Bhavan)	Granger Causality of Diffusion Processes Speaker: Prof. Dr. Jan Freund, Complex Systems Group, ICBM, University of Oldenburg, Germany Abstract: The reconstruction of causal interactions between process components from empirical data, viz. multivariate time series, is not possible from plain cross-correlation analyses but can be done in the context of Granger causality. Operational definitions are based on the assumption that multivariate time series can be viewed as realizations of a class of linear stochastic processes, usually vector autoregressive processes of order p (VAR[p]). For nonlinear dynamics this assumption may be far from justified and transfer entropy (predictive information flow) was devised to treat also strongly nonlinear dynamics – at the expense of diminished statistical power. Here I will present an alternative approach that is based on a local linearization of a nonlinear diffusion processes and that renders a Granger causality map which quantifies local prediction improvement on an attractor. This generalization may prove useful for a characterization of brain dynamics or for the analysis of multivariate data recorded at wind farms.
07.12.2017, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Critical Transitions Due to Shocks Speaker: Prof. Dr. Ulrike Feudel, Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University Oldenburg, Germany Abstract: Natural or technical systems possess often several possible stable states of operation. Linear stability theory is the appropriate tool to study the stability properties of such states with respect to small perturbations. However, in nature perturbations are not necessarily small but are finite in size. We discuss two different methods how to investigate the stability with respect to large perturbations such as single shocks. Both methods aim to determine the distance to the boundary of the basin of attraction or the edge of chaos, respectively. The first method determines the minimal destabilizing perturbation for large dynamical systems such as networks. Besides the size of this perturbations the method allows also to obtain the direction of this perturbation. We illustrate this method using pollinator networks in ecology and energy networks and identify relations between the topology of a network and its stability properties. The second method measures return times to a stable state at the edge of chaos. This is demonstrated for the transition from laminar to turbulent motion in a shear flow.
07.12.2017, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	The Search For the Smallest Chimera Speaker: Prof. Tomasz Kapitaniak, Division of Dynamics, Lodz University of Technology, Lodz, Poland Abstract: We demonstrate that chimera behavior can be observed in small networks consisting of three identical oscillators, with mutual all-to-all coupling. Three different types of chimeras, characterized by the coexistence of two coherent oscillators and one incoherent oscillator (i.e., rotating with another frequency) have been identified, where the oscillators show periodic (two types) and chaotic (one type) behaviors. Typical bifurcations at the transitions from full synchronization to chimera states and between different types of chimeras have been described. Parameter regions for the chimera states are obtained in the form of Arnold tongues, issued from a singular parameter point. Our analysis suggests that chimera states can be observed in small networks relevant to various real-world systems.
25.10.2017, at 12.00 noon Seminar room, PAMU (Kolmogorov Bhavan)	Universal Laws of Thermodynamics Speaker: Manabendra Nath Bera, ICFO, Barcelona, Spain Abstract: Thermodynamics is one of the most successful physical theories ever formulated. Though it was initially developed to deal with steam engines and, in particular, the problem of conversion of heat into mechanical work, it has prevailed even after the scientific revolutions of relativity and quantum mechanics. Despite its wide range of applicability, it is known that the laws of thermodynamics break down when systems are correlated with their environments. In the presence of correlations, anomalous heat flows from cold to hot baths become possible, as well as memory erasure accompanied by work extraction instead of heat dissipation. Here, we generalize thermodynamics to physical scenarios which allow presence of correlations, including those where quantum entanglements are present. We exploit the connection between information and physics, and introduce a consistent redefinition of heat dissipation by systematically accounting for the information flow from system to bath in terms of the conditional entropy. As a consequence, the formula for the Helmholtz free energy is accordingly modified. Such a remedy not only fixes the apparent violations of Landauer's erasure principle and the second law due to anomalous heat flows, but it also leads to a reformulation of the laws of thermodynamics that are universally respected. In this information-theoretic approach, correlations between system and environment store work potential. Thus, in this view, the apparent anomalous heat flows are the refrigeration processes driven by such potentials.
19.09.2017, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Estimating hidden signals violating isotropy underlying CMB maps Speaker: Pavan Kumar Aluri, KIAS, South Korea Abstract: The standard model of cosmology is based on the cosmological principal which states that the universe is homogeneous and isotropic on very large scales. However cosmic microwave background which is a prediction of Big Bang theory is found to have signals of isotropy violation on large angular scales. One of the important aspects of CMB data analysis is to remove the effect of local microwave emission from our own galaxy in order to obtain pristine cosmic CMB signal. In this talk I will introduce a method to estimate hidden signals violating isotropy underlying CMB sky directly from a partial sky (masked CMB sky with some regions of the CMB sky set to zero to avoid bias due to residual contamination). The effect of masking on the estimation process is studied in detail, and an estimator is proposed to directly use the partial sky data accounting for the mask. We then applied it to PLANCK 2015 CMB maps as part of India/IUCAA Planck team. This method is also applicable to recover weak lensing field.
19.09.2017, at 11.30 am Seminar room, PAMU (Kolmogorov Bhavan)	State independent contextuality advances one-way communication Speaker: Debashis Saha, ITPA, University of Gdansk, Poland Abstract: Kochen-Specker theorem (more generally state independent contextuality (SIC)) is one of the most fundamental research areas in quantum physics. We are celebrating the 50th year of this discovery, and the role of quantum contextual correlations has been attracting an increasing attention in quantum information over the years, resulting in a rich variety of investigations. However, all the proposed applications of single system SIC lack in two important aspects. One is the universality of the quantum advantage for each SIC proof and more importantly, the advantages over classical system are in restricted scenarios instead of impossibility of a task itself. This talk presents a new perspective in this line of study by connecting SIC with the advantage of quantum channel over classical in one-way communication. We study a family of one-way communication problem based on orthogonal graphs of SIC sets of vectors. First, we reveal that if the dimension of the communicated system is bounded, sending quantum systems, which correspond to the vectors of each SIC set, is advantageous over classical communication. Then, we propose a general framework of oblivious communication and show that under certain oblivious condition for the same communication task, the quantum strategy corresponds to each Kochen-Specker set outperforms classical communication of arbitrary large dimensional system. The quantum protocol allows the parties to accomplish the communication task perfectly. In the case of classical communication, we present a general method to obtain the best possible strategy. Our results provide a fully operational significance to single system SIC and open up the possibility of quantum information processing based on that.
25.08.2017, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	On thermalization of two-level quantum systems Speaker: Sibasish Ghosh, IMSc, Chennai Abstract: It has always been a difficult issue in Statistical Mechanics to provide a generic interaction Hamiltonian among the microscopic constituents of a macroscopic system which would give rise to equilibration of the system. One tries to evade this problem by incorporating the so-called $H-theorem$, according to which, the (macroscopic) system arrives at equilibrium when its entropy becomes maximum over all the accessible micro states. This approach has become quite useful for thermodynamic calculations using the (thermodynamic) equilibrium states of the system. Nevertheless, the original problem has still not been resolved. In the context of resolving this problem it is important to check the validity of thermodynamic concepts -- known to be valid for macroscopic systems -- in the microscopic world. Quantum thermodynamics is an effort in that direction. As a toy model towards this effort, we look here at the process of thermalization of a two-level quantum system under the action of a Markovian master equation corresponding to memory-less action of a heat bath, kept at certain temperature. A two-qubit interaction Hamiltonian (H_{th}, say) is then designed -- with a single-qubit mixed state as the initial state of the bath -- which gives rise to thermalization of the system qubit in the infinite time limit. We then look at the question of equilibration by taking the simplest case of a two-qubit system A + B, under some interaction Hamiltonian H_{int} (which is of the form of H_{th}) with the individual qubits being under the action of separate heat baths of temperatures T_A, and T_B. Different equilibrium phases of the two-qubit system are shown to appear -- both the qubits or one of them get cooled down. In the passing, we will also comment on thermalization of a qubit using non-Markovian evolution.
07.07.2017, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Periodically driven dynamics using two-rate protocols Speaker: Satyaki Kar,Theoretical Physics Department, Indian Association for the Cultivation of Science, Kolkata Abstract: We study the non-equilibrium dynamics in closed quantum systems periodically driven via time dependent parameters with two fiequencies ω₁ and ω₂ = rω. Tuning of the ratio r there can unleash plenty of dynamical phenomena to occur. Our study includes integrable models like Ising and XY models in d=1 and Kitaev model in d=1 and 2 and can also be extended to Dirac fermions in graphene. We witness the wave-function overlap or dynamic freezing to occur within some small/ intermediate frequency regimes in the (ω,r) plane (with r≠0) when the ground state is evolved through single cycle of driving. However, evolved states soon become steady with long driving and the freezing scenario gets rarer. We extend the formalism of adiabatic-impulse ipproximation for many cycles driving within our two-rate protocol and show the near-exact comparisons at small frequencies. An extension of the rotating wave approximation is also developed to gather an analytical framework of the dynamics at high frequencies. Finally we compute the entanglement entropy in the stroboscopically evolved states within the gapped phases of the system and observe how it gets tuned with the ratio r in our protocol. The minimally entangled states are found to fall within the regime of dynamical freezing. In general, the results indicate that the entanglement entropy in our driven short-ranged integrable systems follow genuine non-area law of scaling and show a convergence (with a r dependent pace) towards volume scaling behavior as the driving is continued for long time.
08.06.2017, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Fermionic dark matter and supernova SN1987A cooling Speaker: Prasanta Kumar Das, BITS Goa Abstract: Light dark matter (1 - 30 MeV) particles which can be pair produced in electron-positron annihilation e^-e⁺ → xx inside the supernova SN1987A core take away the energy released in the supernova SN1987A explosion. Using the Raffelt's criteria on the energy loss rate and using the optical depth criteria on the free streaming of the dark matter fermion, we find that the lower bound on the scale Λ of the dark matter effective theory to be Λ ∼ 1.0E+08 TeV for mx = 30 MeV. We extend our study in q-deformed statistics scenario and study the impact of it on the scale Λ.
20.04.2017, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Highlights from IceCube Neutrino Observatory Speaker: Dr. Debanjan Bose, Sung Kyun Kwan University, South Korea Abstract: IceCube is a cubic-kilometer neutrino observatory buried deep in the ice sheet at the geographic South Pole. A total of 5160 Digital Optical Modules (DOMs) are deployed on 86 strings forming a three dimensional detector array. Over the past decade, South Pole has emerged as a leading site for neutrino astronomy, particle astrophysics and neutrino physics. IceCube's discovery of a diffuse flux of astrophysical neutrinos started a new era of neutrino astronomy. In this talk I will describe IceCube neutrino detector and will discuss some of IceCube's results. Also, an overview will be given of plans to upgrade IceCube in the future.
06.01.2017, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Dense Axion Stars Speaker: Abhishek Mohapatra, The Ohio State University, USA Abstract: Axions can be described by a relativistic field theory with a real scalar field whose self-interaction potential is a periodic function of the field. Low-energy axions, such as those produced in the early universe, can be described more simply by a nonrelativistic effective field theory with a complex scalar field. I discuss how to determine the coefficients in the expansion of the effective potential in powers of the complex scalar field. I also discuss a possible way to systematically improve the effective potential that resums terms of all orders in the complex scalar field. A simple application of this effective potential is to axion stars. If the dark matter particles are axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound systems of axions. The previously known solutions are dilute axion stars,whose mass cannot exceed a critical mass of about 10 to the power (-14) Solar mass. I discuss a possible new branch of dense axion stars whose mass can range from about 10 to the power (-20) Solar mass to about 1 Solar mass. If a dilute axion star with the critical mass accretes additional axions and collapses, it could produce a bosenova, leaving a dense axion star as the remnant.
05.01.2017, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Resolution of a Singularity Problem in Gravity Speaker: Dr. Anupam Mazumdar, Lancaster University, UK & Kapteyn Institute for Astronomy, The Netherlands Abstract: I will show how to resolve cosmological and blackhole singularity problems in the Einstein's theory of gravity at a classical level. In the infrared the theory mimics all the predictions of Einstein's General Relativity. I will then construct a potential quantum theory of gravity - which becomes asymptotically free in the ultraviolet.
02.01.2017, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Magnons in a honeycomb ferromagnet Speaker: Saikat Banerjee, Nordic Institute of Theoretical Physics, Nordita Abstract: The original discovery of the Dirac electron dispersion in graphene led naturally to the question of Dirac cone stability with respect to interactions, and the Coulomb interaction between electrons was shown to induce a logarithmic renormalization of the Dirac dispersion. With the rapid expansion of the list of compounds and quasiparticle bands with linear band touching, the concept of bosonic Dirac materials has emerged. At the single particle level, these materials closely resemble the fermionic counterparts. However, how the changed particle statistics affects the stability of Dirac cones has yet to be determined. Here we study the effect of interactions focusing on the honeycomb ferromagnet - where the quasiparticles are magnetic spin waves (magnons) with the same dispersion as the electrons for graphene. We demonstrate that magnon-magnon interactions lead to a significant renormalization of the bare band structure. The charge neutrality and Dirac spectrum of magnons result in finite lifetime effects with significant momentum dependence near the nodes and a temperature dependent shift of the magnon bands. We also address the question of the edge and surface states for a finite system. We applied these results to chromium tri-halides CrX3 (X = F, Cl, Br and I), the class of ferromagnets where the magnetic Cr atoms are arranged in weakly coupled honeycomb layers. Our theory qualitatively accounts for hitherto unexplained anomalies in neutron scattering data from 40 years ago for CrBr3. We expand the theory of ferromagnets beyond the standard Dyson theory and point to new exciting physics of Bose systems on non-Bravais lattices (e.g. honeycomb).
29.12.2016, at 2.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	Vertical Structure of Disk Galaxies & their Dark Matter Halos Speaker: Dr Arunima Banerjee, IUCAA Abstract: According to the modern theory of galaxy formation, galaxies form because of cooling of baryons and star formation at the centres of gigantic halos of dark matter. The cold neutral hydrogen (HI) layer of the galactic disk serves as an effective tracer of the underlying gravitational potential of the dark matter halo in nearby, edge-on spiral galaxies. In the first part of the talk, I will discuss how the density profile of the dark matter halo can be constrained by using the observed HI rotation curve and the HI vertical thickness, as applied to the superthin low surface brightness galaxy UGC 7321, the Andromeda (M31) and our the Galaxy. In the second part, I will show how the superthin nature of the disk of the stars in the low surface brightness galaxy UGC7321 can be traced back to the presence of a dense and compact dark matter halo in this galaxy. Our findings may have important implications for the cosmology and structure formation history of the universe.
29.12.2016, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Noncommutative spaces with generalised uncertainty principle and their implications in quantum information theory Speaker: Dr Sanjib Dey, Centre de Recherches Mathematiques, Universite de Montreal, Canada Abstract: The existence of space-time noncommutativity is very promising in various fields of modern science. Several different types of noncommutative structure have been suggested depending on their significance in different contexts; such as, quantum gravity, quantum cosmology, string theory as well as quantum mechanics. We discuss about the construction of one such noncommutative framework originating from a mathematical background. The physical reality of such models are ensured by exploiting some standard techniques of PT-symmetric non-Hermitian Hamiltonian systems, which is yet another interesting subject in recent days. Nevertheless, we study some interesting applications of this particular noncommutative structure in different areas of mathematics and physics, particularly, in quantum optics and quantum information theory.
04.05.2016, at 3.30 pm Seminar room, PAMU (Kolmogorov Bhavan)	Existence and Uniqueness of solution of ODE; an overview Speaker: Swarup Poria, Department of Applied Mathematics, University of Calcutta Abstract: The study of existence and uniqueness of solutions became important due to the lack of a general formula for solving nonlinear ordinary differential equations (ODE). Compact form of existence and uniqueness theory appears nearly 200 years after the development of the theory of differential equation. In this talk, we shall discuss briefly about existence and uniqueness of solutions of a first order ODE. Special emphasis will be given on the Lipschitz continuous functions.
22.03.2016, at 3.00 pm Seminar room, PAMU (Kolmogorov Bhavan)	A necessary condition for local distinguishability of two-qudit maximally entangled states completely characterises that of the generalized Bell states for $d = 4$ Speaker: Prof. Sibasish Ghosh, IMSC, Chennai Abstract: The (im)possibility of local distinguishability of orthogonal multipartite quantum states still re- mains an intriguing question. Beyond ${C\!\!\!I}^3 \otimes {C\!\!\!I}^3$, the problem remains unsolved even for maximally entangled states (MES). We develop a very simple necessary condition for the perfect local distin- guishability of any set of MES in ${C\!\!\!I}^d \otimes {C\!\!\!I}^d$. This condition places constraints after the first round of measurement of the LOCC protocol, and, by doing so, reduces the complexity of the distin- guishability problem, particularly for any set of $d$ no. of MES. This necessary condition solves the longstanding problem of the existence of $d$ locally indistinguishable orthogonal states taken from the set of generalized Bell states in ${C\!\!\!I}^d \otimes {C\!\!\!I}^d$ by showing that for d = 4, there indeed exist four locally indistinguishable generalized Bell states. The full classification of sets of four generalized Bell states in ${C\!\!\!I}^4 \otimes {C\!\!\!I}^4$ has been made, and it is shown that any four states from such a set are either locally indistinguishable or distinguishable by one-way LOCC using only projective measurements.
06.01.2016, at 3.00 pm Platinum Jubilee Auditorium	The Neutrino Story Speaker: Sreerup Raychaudhuri, Tata Institute of Fundamental Research Abstract: Neutrinos are the most mysterious particles known and many aspects of neutrinos still remain a mystery. This talk will survey, in simple,nontechnical language, the physics of these elusive particles, starting from their discovery in nuclear beta decay processes to the discovery of neutrino flavours and, most importantly, flavour oscillations which won the 2015 Nobel Prize. The role of neutrinos in astrophysics and cosmology will also be touched upon At the end, we will briefly discuss the upcoming Indian Neutrino Observatory and its physics.
21.12.2015, at 3.00 pm PAMU Seminar Room (Kolmogorov Bhavan)	Dynamical State Reduction Models: Pedagogic Introduction and Advantages Speaker: Sujoy K. Modak, JSPS Fellow, KEK High Energy Accelerator Research Organization, Japan Abstract: Dynamical State Reduction Models are modified version of quantum mechanics which were historically formulated to overcome certain problems associated with the Copenhagen interpretation of quantum mechanics. I shall discuss one promising version of them, known as ``Continuous Spontaneous Localization’’ (CSL) theory. Over the years they have evolved to give predictions that are verifiable/falsifiable. In recent times these theories were also used to explain generation of seeds of cosmic structures during inflation which is otherwise not understood. I shall briefly review these aspects and then mostly concentrate on my own work where a resolution to black hole information paradox is proposed using a tailored version of CSL theory.
08.10.2015, at 3.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Action Principle for General Relativity and its Relation to Null Surfaces Speaker: Sumanta Chakraborty, IUCAA Abstract: Constructing a well-posed variational principle and characterizing the appropriate degrees of freedom that need to be fixed at the boundary are non-trivial issues in general relativity. I will discuss a few toy examples in classical mechanics and field theory before going into general relativity. For spacelike and timelike boundaries I will show that the action principle for general relativity is well posed, only when a suitable counter-term [the Gibbons-Hawking-York (GHY) counter-term] is added to the action principle. Also I will show that the degrees of freedom to be fixed on the boundary are contained in the induced 3-metric. These results, however, do not directly generalize to null boundaries on which the 3-metric becomes degenerate. In this talk I will address the following questions: (i) What is the counter-term that may be added on a null boundary to make the variational principle well-posed? (ii) How do we characterize the degrees of freedom which need to be fixed at the null boundary?
18.09.2015, at 2.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Flat space holography: field theory and gravitational aspects Speaker: Dr. Rudranil Basu, IISER Pune Abstract: The holographic principle, as inspired by string theory is an important concept that has helped in better understanding of various unsolved physical problems which range from strongly interacting quantum field theories to quantum gravity. Much of developments in this field however has been in the context of negatively curved space-time, ie in the guise of AdS/CFT duality. One side of the duality deals with a space-time with gravitational interactions whereas the other side describes a quantum field theory living at the boundary of that space-time. We, on the other hand, are studying how the principle of holography can work for physically relevant flat (as opposed to negatively curved) space-time scenarios. In this talk I will describe advances made both in the gravity side as well as the field theory side. Curiously enough, the field theory, although conformal in nature, is one observed by very fast observers.
15.09.2015, at 2.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Search for Supersymmetry: Some avenues less explored Speaker: Dr. Arindam Chatterjee, IISER Pune Abstract: After the discovery of Higgs at LHC, search for Beyond Standard Model (BSM) Physics is in full swing. Supersymmetric theories provide a well motivated extension of the Standard Model. Apart from addressing the hierarchy problem, R-parity conserving supersymmetric scenarios also assure the stability of the Lightest Supersymmetric particle (LSP). The LSP, if neutral, can be a good Dark Matter (DM) candidate. Therefore, the nature of the LSP, in such scenarios, can be probed or constrained using both Dark Matter (DM) and collider searches. At LHC, the decay of strongly interacting sparticles, which can have large production cross-sections, can lead to different signals for different LSPs. We consider two different scenarios in this context: one featuring a left-sneutrino as the LSP and the other with a neutralino as the LSP. We show that in both cases distinct collider signals from the stop sector may be observed in the (near) future. The viability of these LSPs as Dark Matter candidates are also explored. In the second part of the talk, we will discuss the possibility of accommodating an inflaton candidate within the minimal supersymmetric model in the context of ``inflection-point inflation". Further, we will comment on generic features and constraints on these scenarios in the light of recent data from PLANCK and BICEP.
19.08.2015, at 3.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Quantum Rational Secret Sharing Speaker: Dr. Goutam Paul, Cryptology and Security Research Unit, ISI Abstract: A rational secret sharing scheme is a game in which each party responsible for reconstructing a secret tries to maximize his or her utility by obtaining the secret alone. While there exist schemes for classical rational secret sharing, quantum secret sharing schemes, derived either from quantum teleportation or from quantum error correcting code, do not succeed when we assume rational participants. This is because all the existing quantum secret sharing schemes consider that the secret is reconstructed by a party chosen by the dealer. We, for the first time, propose a quantum secret sharing scheme which is resistant to rational parties. The proposed scheme achieves fairness, correctness and strict Nash equilibrium.
08.07.2015, at 3.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Collective dynamics of non-linear oscillators Speaker: Dr. Punit Parmananda, Physics Department, IIT Bombay Abstract: The dynamics of the Mercury Beating Heart (MBH) system is analyzed experimentally. Subsequently, two such oscillators were coupled and the resultant synchronization phenomena studied. Finally, the collective dynamics for an ensemble of MBH oscillators were investigated, and Kuramoto transitions were verfied experimentally. The dynamics of the Mercury Beating Heart (MBH) system is analyzed experimentally. Subsequently, two such oscillators were coupled and the resultant synchronization phenomena studied. Finally, the collective dynamics for an ensemble of MBH oscillators were investigated, and Kuramoto transitions were verfied experimentally.
01.06.2015, at 3.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Associated Higgs production with a Z boson in the Non-Commutative Standard Model Speaker: Dr. Prasanta Kumar Das, BITS-Pilani Abstract: We Study the associated Higgs production with Z boson at future linear colliders in the framework of the minimal non-commutative standard model. Using the Seiberg-Witten map, we calculate the production cross-section considering all orders of the non-commutative parameter Θμν. We consider the effect of earth’s rotation on the orientation of θμν with respect to the laboratory frame and thus on the total cross-section, it’s azimuthal distribution etc for the machine energy ranging from 0.5 TeV to TeV corresponding to the non-commutative scale Λ ≥ 0.5 TeV.
13.05.2015, at 3.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Universal detection of bi-partite entanglement in measurement-device-independent way Speaker: Prof. Sibasish Ghosh, IMSc Abstract: Whenever a source produces a bi-partite state, how to verify experimentally whether the state is entangled? One generally performs measurement -- to be realized locally on the individual subsystems -- of some observable (called as entanglement witness operator (EWO)) on the state for this verification. Unfortunately, the detectors themselves may not be reliable to the extent that even a separable state may be revealed as an entangled one. Is it at all possible to witness entanglement in a measurement-device-independent (MDI) way? The answer turned out to be in the affirmative through a recent work by Branciard et al. [Phys. Rev. Lett., vol. 110, pp. 060405 (2013)], provided a form of an EWO, witnessing the entanglement in the `given' state is known beforehand. It is important to note here that any such EWO depends generally, on the given state with an exception in the case of two-qubit states. In fact, it was shown by Augusiak et al. [Phys. Rev. A, vol. 77, pp. 030301 (2008)] that entanglement in an arbitrary two-qubit state can be witnessed by a state-independent EWO provided four copies of such a state are available. Using this latter result, we give a scheme here to detect entanglement in any two-qubit state in a state-independent but MDI way. We also provide here a scheme to distinguish between PPT and NPT states in state-independent but MDI way -- valid for any dimension. Finally, we conjecture that entanglement in any bi-partite state can always be witnessed in a state-independent but MDI way, whatever be the dimension of the system.
11.05.2015, at 3.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	PT symmetric optical lattices : some intriguing features Speaker: Dr. Anjana Sinha, Jadavpur University Abstract: With the experimental verification of PT symmetric concepts in optics, PT symmetric optical lattices have opened up a very interesting area of study in the last few years. These systems have complex refractive index of the form n(x) = n0+nR(x)+inI(x) with nR,I less than n0 . The intriguing behaviour of the scattering coefficients — reflection \|T\| and transmission \|R\| — is quite different from what we observe in conventional quantum me- chanics. The scattering amplitudes do not necessarily add up to unity. Rather, they obey a modified relationship. Furthermore, their behaviour depends on the direction of the incident wave, and also on the parameters in the optical potential. In case of spontaneous breakdown of PT symmetry at some value of the potential parameter, one observes the fascinating phenomena of Spectral Singularity, where reflection and transmission coeffi- cients tend to diverge. The talk will discuss some interesting features related to scattering in PT symmetric optical devices.
08.05.2015, at 3.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Constraining the Nature of Dark Energy from Cosmological Observations Speaker: Dr. Ujjaini Alam Abstract: Dark energy is one of the most tantalizing mysteries in current cosmological research. A host of observations confirm that about two-thirds of the energy content of the universe comprises of this negative-pressure ''dark energy'' component that causes the expansion of the universe to accelerate. In my talk, I will explore two distinct facets of dark energy research. Many different theoretical models have been suggested for dark energy. One aspect of my research is to study these theoretical models, such as early dark energy and modified gravity models, and constrain them in light of current observations. A second approach to the dark energy problem is to study the various observations available to us with different statistical tools, and optimize these methods for obtaining maximum information on the dark energy parameters. Using these two complementary approaches in conjunction, we expect to shed light on the nature of dark energy.
27.04.2015, at 3.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Exploring Novel Quantum Phenomena in Photonic Settings: From Fundamentals to Technological Applications Speaker: Dr. Somnath Ghosh, Calcutta University Abstract: Corroborating the analogy between non-Hermitian quantum system and counterpart optical geometries with suitable amount of simultaneous gain and loss, I plan to discuss an innovative scheme for asymmetric mode conversion in a coupled optical system under certain condition in the strong coupling regime (beyond the PT symmetry limit) exploiting singularities (in eigen values and eigen vectors) associated with avoided crossings (in the regime where adiabatic evolution fails) as an efficient tool. Novel propagation dynamics of light wave through this special optical structure is evident, which is being explored in the context of optical isolation for integrated/ on-chip photonics applications. From fundamental physics point of view and applications in photonics like realizing compact random lasing in one dimensional disordered system (longitudinal direction mapped onto time), I plan to focus on my latest findings to demonstrate that the simultaneous presence of spatial and refractive index disorder favors Anderson localization of light. This study has revealed several underlying interesting features of light confinement to a localized state in such a medium of finite length and showed that beyond the point of localization, light indeed propagates without any diffractive spread in the transverse direction in a disordered lattice, a feature that mimics waveguide-like propagation. The hallmark stochastic nature of the phenomena has been encountered in both simulations and experiments using ultrafast laser inscription (ULI) technique.
24.04.2015, at 12.30 pm PAMU Seminar Room (Kolmogorov Bhavan)	Generating Finite Dimensional Integrable Nonlinear Dynamical Systems and their Quantization Speaker: Prof. M. Lakshmanan, FNA,FTWAS, Centre for Nonlinear Dynamics, Bharathidasan University, Tiruchirapalli Abstract: We present an overview of some recent progress made in identifying and generating finite dimensional integrable nonlinear dynamical systems, exhibiting oscillatory and other solution properties, including quantum aspects. Particularly we will concentrate on Lienard type nonlinear oscillators and their generalizations and their coupled versions. Specific systems include Mathews-Lakshmanan oscillators, modified Emden equations, isochronous oscillators and generalizations. Nonstandard Lagrangian and Hamiltonian formulations of some of these systems will be briefly touched upon. Nonlocal transformations and linearization aspects will be briefly discussed.
21.11.2014, at 3.00 pm NAB 2 (Kolmogorov Bhavan)	Ancilla assisted suppression of decoherence Speaker: Sibasish Ghosh, IMSc Chennai Abstract: Most of the quantum mechanical systems are open in nature -- they often interact with their surroundings quite fast, leading to decoherence. This issue of decoherence is a major obstacle in physical realisations of different quantum information processing schemes. It not only destroys quantum coherence in individual subsystems, but as a result of that, it also (in general), destroys entanglement among the subsystems. Different mechanisms have been developed -- mostly specific to systems concerned -- to control this decoherence effect, most of which aim at weakening the system--environment interaction in a controlled manner. In the present work, we instead, aim at inserting an ancillary system so that the environment acts jointly on the system and the ancilla. Considering Markovian type environmental effect, we find that one can suppress both decoherence as well as decay of entanglement by this method. Moreover, we find that larger the size of the ancilla, better is the suppression mechanism.
11.11.2014, at 3.00 pm NAB 2 (Kolmogorov Bhavan)	Numerical Simulation with relativistic equation of state of astrophysical plasma Speaker: Indranil Chattopadhyay, Aryabhatta Research Institute for observational sciences (ARIES) Abstract: We discuss computational fluid dynamics in general and how they are applied in various astrophysical scenario. We focus on how to incorporate the relativistic equation of state of multi-species fluid in relativistic hydrodynamic code. We show that in the trans-relativistic temperature regime, composition plays a very important role in the temporal evolution of relativistic hydrodynamics. We discuss the impact this would have on observations.
07.11.2014, at 3.00 pm NAB 2 (Kolmogorov Bhavan)	Spinor field and anisotropic cosmological models Speaker: Bijan Saha, D.Sc, Joint Institute for Nuclear Research Dubna, Moscow reg. Abstract: Within the scope of a Bianchi type-I anisotropic cosmological model we study the evolution of the Universe filled with nonlinear spinor field. It is found that due to some specific behavior of the spinor field it imposes some restriction either of spinor field components or on metric functions. It is found that for some suitable choice of parameters the spinor field can give rise to singularity free spacetime; accelerate the isotropization process; explain the late time accelerated mode of expansion and simulate perfect fluid, quintessence, Chaplygin gas and different type of Dark energy.
28.08.2014, at 3.30 pm NAB 1 (Kolmogorov Bhavan)	Dynamical Localization in quantum spin-fermion systems: Suppressing the Relaxation of quantum magnets by a coherent periodic drive Speaker:Dr. Analabha Roy , SINP. Abstract: Dynamical localization is one of the most startling manifestations of quantum interference, where the evolution of a simple system is frozen out under a suitably tuned coherent periodic drive. In this talk, I shall demonstrate that such freezing occurs even in the presence of extensive disorder in a many-body system. I consider a disordered quantum Ising chain where the transverse magnetization relaxes exponentially with time with a decay time-scale [image: \tau] due to random longitudinal interactions between the spins. Using Floquet theory and Renormalization Group techniques, I will show that this relaxation can be slowed down ([image: \tau] is enhanced) by orders of magnitude due to employing periodic drives at certain specific values of frequencies and amplitudes (the freezing condition) regardless of the initial state. Under the freezing condition, [image: \tau] diverges exponentially with the drive frequency [image: \omega]. The results can be easily extended to a larger family of disordered fermionic and bosonic systems. I will then discuss universality in the relaxation behavior, generalizations to open quantum systems, as well as using this phenomenon to prevent the propagation of errors in systems of quantum bits.
23.07.2014, at 15.30 PAMU Computer Lab (Kolmogorov Bhavan)	Minimal state-dependent proof of measurement contextuality for a qubit Speaker: Dr. Sibasish Ghosh, IMSc, Chennai . Abstract: We show that three unsharp binary qubit measurements are enough to violate a generalized noncontextuality inequality, the LSW inequality, in a state-dependent manner. For the case of trine spin axes we calculate the optimal quantum violation of this inequality. Besides, we show that unsharp qubit measurements do not allow a state-independent violation of this inequality. We thus provide a minimal state-dependent proof of measurement contextuality requiring one qubit and three unsharp measurements. Our result rules out generalized noncontextual models of these measurements which were previously conjectured to exist. More importantly, this class of generalized noncontextual models includes the traditional Kochen-Specker (KS) noncontextual models as a proper subset, so our result rules out a larger class of models than those ruled out by a violation of the corresponding KS-inequality in this scenario.
09.07.2014, at 15.00 PAMU Computer Lab (Kolmogorov Bhavan)	Resurrecting left-sneutrino Dark Matter in SUSY in the light of direct Dark Matter searches Speaker: Dr. Arindam Chatterjee , HRI Allahabad . Abstract: In the minimal supersymmetric standard model (MSSM) the lightest superpartner of the left-handed neutrinos is ruled out as a Dark Matter candidate because of its large elastic cross-section with the nucleus mediated via Z-boson. We resurrect it by extending the MSSM with two (heavy) triplets of opposite hyper-charge. The addition of these triplets not only generates small Majorana mass for the left-handed active neutrinos, but also makes sneutrino (LSP) a candidate for dark matter (of inelastic type). We then discuss the relevant parameter space which can give rise to the right amount of (thermal) relic abundance while satisfying the current direct detection constraints from Xenon100 and LUX.
25.06.2014, at 15.00 PAMU Seminar Room (Kolmogorov Bhavan)	Device-independent quantum key distribution based on Hardy’s paradox Speaker: Dr. Ramij Rahaman, University of Allahabad . Abstract: We present a secure device-independent quantum key distribution (QKD) scheme based on Hardy’s paradox. Hardy’s paradox uses four conditions impossible for classical systems, but satisfied by predictions for a unique quantum two-particle state. In comparison with protocols based on Bell inequalities, our scheme has several novel features: (a) The bits used for the secret key do not come from the results of the measurements on an entangled state but from the choices of settings which are harder for an eavesdropper to influence; (b) Instead of a single security parameter (a violation of some Bell inequality) a set of them is used to estimate the level of trust in the secrecy of the key. This further restricts the eavesdropper's options. We prove the security of our protocol for both ideal and noisy cases.
28.04.2014, at 15.30 NAB 1 (Kolmogorov Bhavan)	Applicability of First Law for Rindler Horizon Speaker: Dr. Srijit Bhattacharjee, Department of Physics, IISER Mohali. Abstract: The physical process version of the first law for black holes states that the passage of energy and angular momentum through the horizon results in change in area κ/8π ∆A = ∆E − Ω∆J, so long as the passage is quasistationary. The validity of the process first law crucially depends upon the control over the horizon shear and expansion such that they remain small. I will discuss how such control can be established in the case of a weakly self-gravitating object crossing Rindler horizon.
15.04.2014, at 15.30 NAB 1 (Kolmogorov Bhavan)	Turbulence in mobile-bed streams Speaker: Prof. Subhasish Dey, Indian Institute of Technology Kharagpur. Abstract: The study is devoted to quantify the near-bed turbulence parameters in mobile-bed flows with bed-load transport. A reduction in near-bed velocity fluctuations due to the decrease of flow velocity relative to particle velocity of the transporting particles results in an excessive near- bed damping in Reynolds shear stress (RSS) distributions. The bed particles are associated with the momentum provided from the flow to maintain their motion overcoming the bed resistance. It leads to a reduction in RSS magnitude over the entire flow depth. In the logarithmic law, the von Kármán coefficient decreases in presence of bed-load transport. The turbulent kinetic energy budget reveals that for the bed-load transport, the pressure energy diffusion rate near the bed changes sharply to a negative magnitude, implying a gain in turbulence production. According to the quadrant analysis, sweep events in mobile-bed flows are the principal mechanism of bed-load transport. The universal probability density functions for turbulence parameters given by Bose and Dey have been successfully applied in mobile-bed flows..
06.02.2014	A short overview on Higgs physics at the Large Hadron Collider. Speaker: Dr Siba Prasad Das, Institute of Physics , Bhubaneswar.
Sept. 17, 2013	Turbulence in Loose Boundary Streams Speaker: Sankar Sarkar, Sikkim Manipal Institute of Technology , INDIA.
Sep. 6, 2013	Exact results in two dimensional hydrodynamics with gauge and gravitational anomalies. Speaker: Prof. Rabin Banerjee, SNBNCBS Kolkata,, India. Abstract: We give the exact constitutive relations that express the stress tensor and the charged current in terms of the fluid variables in two dimensional hydrodynamics in the presence of gauge and gravitational anomalies. We distinguish between anomalies in chiral and nonchiral theories. The interplay between conformal invariance and diffeomorphism invariance is highlighted. The modifications in the ideal fluid constitutive relations in the presence of chirality are illustrated.
June 04, 2013	The non-linearity of the Cepheid Period-Luminosity relation. Speaker: Prof. Shashi Kanbur, SUNY Oswego, USA. Abstract: The Cepheid Period-Luminosity relation is of paramount importance in developing an extra-galactic distance scale that is independent of the Cosmic Microwave Background. Developing such an independent distance scale that is accurate to less than 3% is important in placing constraints on the dark energy equation of state. For the last 70 years, the assumption has been that the PL relation is linear. Here we review recent evidence supporting a nonlinear PL relation, the impact on estimates of Hubble's constant and on stellar pulsation and also comment on recent advances in the statistical description of the quantitative structure on variable star light curves.
May 9, 2013	Art of writing academic article and modern trends in publishing. Speaker: S. K. Venkateshan, TNQ Books and Journals, India. Abstract:
May 10, 2013	Turbulance in fluid flows and the breaking of implicit symmetries. Speaker: S. K. Venkateshan, TNQ Books and Journals, India. Abstract:
February 25, 2013	Study of Astrophysical Sources in Very High Energy Regime Using Ground Based Gamma-ray and Neutrino Telescopes. Speaker: Dr. Debanjan Bose, Vrije Universiteit Brussel, Belgium. Abstract: In this presentation I will talk about sources like pulsars, AGN and GRBs in very high energy regime. At these energies we study non-themal Universe. From observations we know that relativistic effects are taking place inside these objects. These sources emit high energy gamma-rays and are also expected to emit neutrinos. I will explain detection principle of gamma-rays and neutrinos with earth based detectors. I will also discuss some important observations for the above mentioned sources with ground based Cherenkov telescopes and IceCube neutrino observatory.
January 10, 2013	Dark Energy Model Building and Observational Signatures Speaker: Dr. Anjan Ananda Sen, Jamia Millia Islamia, New Delhi, India. Abstract: In this talk I shall review the current research on the late time acceleration of the Universe, which is one of the most challenging problems for cosmologists at present. I shall review different approaches to explain such a late time acceleration, in particular the scalar field models. I shall also review the current status of the observational aspects for the dark energy models.
November 30, 2012	Statistical physics of glasses Speaker: Prof. Deepak Dhar, Tata Institute of Fundamental Research, Mumbai. Abstract: In this talk, after a general introduction to the problem of describing the glassy state, I will describe our work on a simple model where we explicitly take into account the fact that ergodicity is broken, and one should calculate averages of physical quantities using restricted partition functions, that sum only over accessible states of the system.
November 23, 2012	Black Holes in Your Bathtub Speaker: Dr. Tapas K Das, Harish Chandra Research Institute, Allahabad. Abstract: I plan to talk about the analogue gravity phenomena, where one can create certain astrophysical (black hole) and cosmological (Friedmann Robertson Walker expanding Universe) spacetime in the laboratory, using classical (water in a bathtub or wash basin, for example) or quantum (Bose Einstein Condensates or liquid Helium, for example) fluids. In a series of papers, I have recently developed, for the first time in the literature, an analytical model which studies the analogue spacetime embedded within the relativistic accreting fluid onto astrophysical black holes. This is a unique example of the classical analogue model naturally found in the Universe where the analogue space time is studied in the strong gravity environment. Such a configuration is the only analogue system available so far which contains both the gravitational as well as the acoustic horizons.
November 15, 2012	Probing the Universe's first light: Statistical detection of reionization 21 cm signal Speaker: Dr. Kanan K. Datta, , Stockholm University, Sweden. Abstract: The cosmic reionization is one the most important missing pictures in the history of our Universe. It is believed that during this epoch the first sources of light (e.g first stars, quasars) formed in the Universe and they subsequently reionized the neutral hydrogen in the intergalactic medium. Radio interferometric observations of redshifted 21-cm radiation are considered to constitute the most promising tool to probe the reionization epoch. The first generation radio telescopes (e.g, GMRT, LOFAR, MWA) are trying to detect the signal statistically. I will discuss the statistical quantities that will be measured by such observations. The statistical detection of ionized regions around bright reionizing sources by means of a matched filter technique will also be discussed. At the end I will also discuss constraints on reionizing source parameters that can be achieved by instrument like LOFAR.
July 9, 2012	Parameter estimation and data analysis in Cosmology Speaker: Trina Chakraborty, Indian Statistical Institute, India Abstract: The observational evidence for the current accelerated expansion of the universe is presented. Emphasis has been laid on a number of scalar field dark energy models besides the conventional cosmological constant. To verify the signatures of dynamical dark energy models, diagnostic parameters will be discussed in details and how they are extracted out from observations. Further, methodology for estimation of various cosmological parameters from single dataset or combination of datasets will be presented.
July 9, 2012	Field theory and particle physics aspect of early universe Speaker: Sayantan Choudhury, Indian Statistical Institute, India Abstract: We propose two models of inflation in the framework of braneworld and standard cosmology. First starting from bulk supergravity we construct the inflaton potential on the brane and employ it to investigate for the consequences to inflationary paradigm. To this end, we derive the expressions for the important parameters in brane inflation, which are somewhat different from their counterparts in standard cosmology. We have studied extensively reheating phenomenology, which explains the thermal history of the universe and leptogenesis through the production of thermal gravitino. Next we propose another model of inflation originated from gauge invariant MSSM flat directions comprising of QQQL, QuQd, QuLe and uude. To this end, we further estimate the observable parameters for both the models and find them to fit well with recent observational data. Finally, we analyze one loop RG flow to determine the appropriate parameter space for inflation.
07-06-2012	Energy Efficiency in Architectural Designs in the Indus Valley Civilization: Lessons learnt for new designing Speaker: Satyajit Ghosh , University of Leeds, U.K. Abstract: The Indus Valley civilization flourished between 2750-1900 B.C. We present a case study for Lothal, an extension of the Indus Valley civilization currently located in the state of Gujarat in India. Their double storied buildings were clustered around geometrical grids comprising of three divisions, including a citadel, a middle town and a lower town. An on-site visit revealed that the buildings were suitably oriented for maximum solar gains. The standardised stone blocks used had thermal transmissivities ("U" values in today's architectural parlance) that retained indoor coolth substantially. The rectangular building forms ensured the presence of active and passive zones even then. As Mechanical engineers, we have used Autodesk Ecotect Analysis to calculate Daylight Factors, Solar Radiation and Water Usage. We have explored quantitatively the fascinating world of light and shadows, coolth and warmth, and obtained answers for the following questions: 1. Were the orientation and the clustering perfect in the city of Lothal? 2. Can these architectural designs prevail with some modifications in today's times? After all, modernists believe that vernacular architecture can also be sustainable. 3. How feasible is it to use engineered eco-fabrics in modern settlements (keeping in mind the versatility of traditional fabrics)? In this paper we shall present a prototype of a new proposed city called "The Sanctuary" housing 40,000 inhabitants (possibly the population in Lothal in 2500 B.C.). Our analysis shows how architectural structures adapt to driving rain, the ingress of winds and a glaring sun. Ecotect calculations elucidate contrasting patterns of energy use in residential areas of Lothal vis-a-vis the dwellings in The Sanctuary. To our knowledge, this is a first study exploring energy efficiency in Lothal.
21-05-2012	Floating orbits around rotating black holes and imprints of massive scalars Speaker: Sayan Chakrabarti, Instituto Superior Tecnico, Lisbon, Portugal. Abstract: In this talk I plan to discuss the coupling of massive scalar fields to matter in orbit around rotating black holes. It is generally expected that orbiting bodies will lose energy in gravitational waves, slowly inspiralling into the black hole. Instead, we show that the coupling of the field to matter leads to a surprising effect: because of superradiance, matter can hover into "floating orbits" for which the net gravitational energy loss at infinity is entirely provided by the black hole's rotational energy. Orbiting bodies remain floating until they extract sufficient angular momentum from the black hole, or until perturbations or nonlinear effects disrupt the orbit.
15-05-2012	*Zero discordness of initial system-environment correlation versus complete positivity of the dynamical map of the system* Speaker: Sibasish Ghosh, The Institute of Mathematical Sciences, India Abstract: For more than three decades, the scaling theory of localization asserted that a two dimensional (2D) system of quantum particles with even infinitesimal disorder cannot have a metallic state : it will always be localized. When recent experiments uncovered a metal-insulator transition (MIT) in two-dimensional electron gases in high-mobility semiconductor hetero-structures, this view was challenged. However, whether a true MIT exists as a quantum phase transition in these systems is still controversial. We have used extensive Quantum Monte Carlo (QMC) simulations to show that, in a related model (the Anderson-Hubbard model in two dimensions) a quantum phase transition exists between a metallic state and an Anderson-localized state. We will also discuss the possible nature of this metallic state, connect this transition with the superconductor-insulator transition (SIT) in 2D, and discuss surprising magnetic properties of a 2D fermionic system when both interaction.
10.05.2012	*Presence of Quantum diffusion in two dimensions : effect of inter-particle interactions on Anderson localization* Speaker: Prabuddha Chakraborty, ISI, Chennai Abstract Quantum systems are quite fragile -- they often interact with their respective environments, which eventually leads to non-unitary dynamics of the states of the systems. Although this dynamics is non-unitary, it can be realized as a unitary dynamics of the system and its environment together and thereby ignoring the environmental degrees of freedom. In this way of realization, the non-unitary dynamics is guaranteed to be a physical evolution (i.e., a completely positive map) allowed by the rules of Quantum Mechanics if the initial joint state is taken to be the tensor product of any state of the system and a fixed state of the environment. In recent years, there has been a growing interest in relaxing the initial correlation between the system and the environment to the extent where the non-unitary dynamical map would still remain completely positive (CP), and the zero discordness of the initial correlation has been proposed to be the characterising feature for the CP-ness of the dynamical map. We argue in this paper that for the CP-ness of the dynamical map, the aforesaid product structure of the initial correlation is inevitable.
27.04.2012	*Scattering of water waves by a thin elastic vertical plate* Speaker: Rumpa Chakraborty, ISI, Kolkata Abstract The problem of scattering of water waves by a thin elastic vertical plate either partially immersed or completely submerged in infinitely deep water or in finite depth water, is investigated here. Within the framework of linearised theory of water waves. The boundary condition on the elastic plate is derived from the Bernoulli-Euler equation of motion of the plate and is given as the normal velocity on the plate to be prescribed in terms of an integral involving the difference of potentials describing the motion in the two sides of the plate, multiplied by an approximate Green's function. The two ends of the barrier may be clamped or free, and the end conditions play a crucial role in the construction of the Green's function. The reflection and transmission coefficients are obtained in terms of integrals involving three unknown functions satisfying two Fredholm integral equations. The integral equations are solved by the Nystrom method and the numerical values of the reflection and transmission coefficients are depicted graphically in a number of figures.