Posters Selected for Workshop-3
Title	First name		Last name	Affiliation	Abstract
Dr.	Sayantan		Choudhury	Max Planck Institute for Gravitational Physics, Albert Einstein Institute,Potsdam	Bose-Fermi Chern-Simons Dualities in the Higgsed Phase\n\nIt has been conjectured that fermions minimally coupled to a Chern-Simons gauge field define a conformal field theory (CFT) that is level-rank dual to Chern-Simons gauged Wilson-Fisher Bosons. The CFTs in question admit relevant deformations parametrized by a real mass. When the mass deformation is positive, the duality of the two deformed theories has previously been checked in detail in the large N limit by comparing explicit all orders results on both sides of the duality. In this paper we perform a similar check for the case of negative mass deformations. In this case the bosonic field condenses triggering the Higgs mechanism. The effective excitations in this phase are massive W bosons. By summing all leading large N graphs involving these W bosons we find an all orders (in the ’t Hooft coupling) result for the thermal free energy of the bosonic theory in the condensed phase. Our final answer perfectly matches the previously obtained fermionic free energy under the conjectured duality map.
Mr.	SAMIM		AKHTAR	Indian Institute of Technology,Madras	In this work, the prime objective is to study non-locality and long-range effect of two-body correlation in an open quantum system (OQS) by using quantum entanglement from various information-theoretic measures in the static patch of De Sitter space. The OQS is described by two entangled atoms surrounded by a thermal bath which is modelled by a massless probe scalar field. The time evolution of the reduced subsystem density matrix is obtained by partially tracing over the bath field and constructing the GSKL Master equation. Using Schwinger-Keldysh formalism the Wightman functions for probe massless scalar field are computed. Using this result along with the large time equilibrium behaviour the analytical solution is then obtained for the reduced density matrix. Further using the solution various information-theoretic measures like Von-Neumann entropy, Renyi entropy, logarithmic negativity, entanglement of formation, concurrence and quantum discord are computed in a static patch of De Sitter space. Finally, violation of Bell-CHSH inequality is studied which is the key ingredient to understand non-locality in primordial cosmology.
Mr.	SHIBENDU		GUPTA CHOUDHURY	INDIAN INSTITUTE OF SCIENCE EDUCATION AND RESEARCH KOLKATA	The role of the Raychaudhuri equation in the big picture of gravitational collapse and Critical Phenomena has been studied.\nAs a model we have considered a conformally flat space time minimally coupled with a scalar field along with the presence of a fluid. The nature of the evolution of the spacetime is found to be dictated by the focusing condition which follows from Raychaudhuri equation. Generic conditions regarding the dynamics of the system can be provided using the Raychaudhuri equation. These conditions are useful in the cases where it is difficult to find an exact solution. After that, we have worked out exact solutions for the metric for some special cases with simplifying assumptions. It is shown that the conclusions from the Raychaudhuri equation are consistent with those from the exact solutions for the cases, mentioned. It seems that there is a connection between the focusing condition and the Critical Phenomena.
Dr.	Samarjit		Chakraborty	Department of Physics, St. Xavier	In this paper we investigate the entropy of the free gravitational field for a given epoch for some well-known inhomogeneous and/or anisotropic cosmologies. We use the definition of gravitational entropy proposed by Clifton, Ellis and Tavakol, where the 2-index square root of the 4-index bell Robinson tensor is taken to be the energy momentum tensor for the free gravity. We transparently show that in the vicinity of the initial singularity, the ratio of energy density of free gravity to that of matter density goes to zero, validating Penrose conjecture on Weyl curvature.
Mr.	Shivang		Goyal	Indian Inst. of Tech., Ropar	We report a non-trivial feature of the vacuum structure of free massive or massless Dirac fields in the hyperbolic de Sitter spacetime. Here we have two causally disconnected regions, say R and L separated by another region, C. We are interested in the field theory in R union L, in order to understand the long range quantum correlations between R and L. There are local modes of the Dirac field having supports individually either in R or L, as well as global modes found via analytically continuing the R modes to L and vice versa. However, we show that unlike the case of a scalar field, the analytic continuation does not preserve the orthogonality of the resulting global modes. Accordingly, we need to orthonormalise them to preserve the canonical anti-commutation relations. A general form of this orthonormalisation is achieved via introducing a spacetime independent continuous parameter, theta_RL. Thus interestingly, we obtain a naturally emerging one-parameter family of alpha-like de Sitter vacua. The values of theta_RL yielding the usual thermal spectra of massless created particles are pointed out. Next, using these vacua, we investigate both entanglement and Renyi entropies of either of the regions and demonstrate their dependence on theta_RL.
Mr.	Subhajit		Barman	Indian Institute of Science Education and Research Kolkata	Title: "A consistent search for the Hawking effect for extremal Kerr black holes". Abstract: "It is believed that extremal black holes do not emit Hawking radiation as understood by taking extremal limits of non-extremal black holes. However, it is debated whether one can make such conclusion reliably starting from an extremal black hole, as the associated Bogoliubov coefficients which relate ingoing and outgoing field modes do not satisfy the required consistency condition. We address this issue in a canonical approach. For extremal Kerr black holes, we show that the required consistency condition is satisfied in the canonical derivation and it produces zero number density for Hawking particles. We also point out the reason behind the reported failure of Bogoliubov coefficients to satisfy the required condition."
Mr.	Surajit		Kalita	Indian Institute of Science, Bangalore	This talk will primarily be based on JCAP 09 (2018) 007. Einstein's general theory of relativity is an incredible theory to explain various astrophysical phenomena e.g. solar system etc. and early universe cosmology. It provides an immense understanding of the physics of various compact objects e.g. black holes, neutron stars, quark stars etc. However, some recent observations in cosmology and also compact objects question the complete validity of the general theory of relativity in extremely high-density regions. Again we know that a white dwarf, as it pulls matter from its companion star, gives rise to type Ia supernova (SNIa). At a certain mass, known as Chandrasekhar mass limit (currently accepted value is 1.4 solar mass for a carbon-oxygen white dwarf), white dwarf becomes unstable and it burns out without leaving any remnant behind. Nevertheless, some recent astrophysical observations argue that the value of the Chandrasekhar mass limit has to be violated. Howell et al. (Nature 443, 308, 2006), Scalzo et al. (Astrophys. J. 713, 1073, 2010) etc. detected extremely high luminous supernovae which they have argued to be originated from white dwarf of mass as high as 2.8 solar mass. On the other hand, Filippenko et al. (Astron. J. 104, 1543, 1992), Modjaz et al. (PASP 113, 308, 2001) etc. have detected supernovae with extremely low luminosity which had to be originated from white dwarf of mass as low as 0.5 solar mass. Das and Mukhopadhyay, (JCAP, 05, 2015, 045) showed for the first time that these two classes of the white dwarf can be explained using the modified theory of Einstein's gravity. They used Starobinsky's f(R) gravity model to explain these phenomena. In the talk, I will explore how these phenomena can be explained using various forms of f(R) gravity. Here I will use some properties of the white dwarf to explain these phenomena rather varying the parameters of the model.
Mr.	Avijit		Chowdhury	Indian Institute of Science Education and Research Kolkata	Title: Hawking emission of charged particles from an electrically charged spherical black hole with scalar hair\n\nAbstract: A static spherically symmetric black hole usually turns out to be either a Schwarzschild black hole or a Reissner-Nordstro ̈m black hole. This result was summarised by Ruffini and Wheeler as the so-called no hair conjecture which states that for a spherically symmetric black hole only the information about mass (M) and electric charge (e) of the black hole is available for an external observer. In this work, we calculate the emission rate of charged particles from an asymptotically flat charged spherically symmetric black hole endowed with a scalar hair using a semi-classical tunnelling formalism. We observe that the total entropy of the black hole contains an energy-dependent part due to the scalar charge. The upper bound on the charge-mass ratio of the emitted particles is also observed to decrease with the scalar charge as well.
Dr.	Aalok		Pandya	Department of Physics, JECRC University, Jaipur 303905 India	Title: Curvature, Torsion and the Geometry of Serret-Frenet Formulae in Geometric Quantum Mechanics\nAbstract: \nFormulation of curvature and torsion in Quantum Geometrodynamics is discussed. Torsion in quantum evolution for symmetric states is found to be:\n$tau^2=frac {langle H^6rangle}{langle H^4ranglelangle H^2rangle}$. Curvature in the quantum evolution formulated earlier by Brody and Houghston in terms of moments of Hamiltonian as $kappa^2=frac {langle H^4rangle}{langle H^2rangle^2}-frac {langle H^3rangle^2}{langle H^2rangle^3}$ is verified. Thus, the formulation of curvature in quantum evolution is reassuring in more than one ways. The Geometry of Serret-Frenet formulae is recast in the context of Geometric Quantum Mechanics. The Geometry of quantum neighborhood also leads to the formulation of curvature and torsion during quantum evolution. Estimator problem when subjected to neighborhood test brings about many significant results. Fourth order term in the quantum neighborhood test carries information of curvature whereas the sixth order term conveys significant information regarding torsion. Interestingly, expressions of curvature as well as torsion as described in this exercise for Quantum Geometrodynamics are experimentally measurable quantities.\nKey-Words: Curvature. Torsion. Quantum Gravity. Serret-Frenet Formulae. Geometrodynamics.
Dr.	BALENDRA	PRATAP	SINGH	Uttaranchal University Dehradun	We study the shadow of rotating charged black holes in the presence of quintessence. The shadow of a rotating black hole is a distorted circle and in our study, we find that the shape and size of the black hole shadow depend on four parameters, i.e., charge $q$, the spin parameter $a$, quintessential field parameter $omega_q$ and normalization factor $c$. The parameter $omega_q$ can take the value between $-1<omega_q<-1/3$ and related with pressure $p$ and density $rho_q$ by the equation of state $p=omega_q rho_q$. We derive the complete geodesic structure of photon near black hole using the Hamilton-Jacobi equation and Carter constant separable method. We relate celestial coordinate to geodesics equation and plot the contour of the black hole shadow. We compare our results with the standard Kerr-Newman black hole and find that for a fixed value of $a$ and $q$, the black hole shadow decreases and get distorted. The area of the photon sphere is equal to the high-energy absorption cross-section due to the optical properties of the black hole. Based on this assumption we calculate the energy emission rate of the black hole.
Mr.	SATYAKI		CHOWDHURY	NISER,BHUBANESHWAR	Title-Quantum entanglement in De-Sitter space from open two atomic system \nAbstract-In this work,we study the phenomenon of quantum entanglement from different quantum information theoretic measures in De-Sitter space for a Open Quantum System(OQS) described by two entangled atoms surrounded by a thermal bath, modelled by a mass-less probe scalar field. First of all, we partially trace over the bath degrees of freedom from the total OQS setup and construct the Gorini Kossakowski Sudarshan Lindblad (GSKL)master equation, which describes the time evolution of the reduced density matrix. This GSKL master equation is characterized by two significant components, these are- Heisenberg spin chain interaction or Lamb Shift and the quantum dissipator or Lindbladian operator.To fix the form of both of these components, using Schwinger Keldysh formalism we compute the two atomic Wightman functions at finite temperature, their Fourier and Hilbert trans-forms for probe massless scalar field. Using the large time equilibrium behaviour we obtain the solution for each of the time dependent entries of reduced density matrix. Further using this solution we compute Von-Neumann entanglement entropy, Re’nyi entropy, logarithmic negativity, entanglement of formation,concurrence and quantum discord to study the effect of long range quantum correlations in quantum entanglement in the background De Sitter space-time. Finally, we have studied violation of Bell-CHSH inequality in De Sitter space,which is the key ingredient to study non-local features
Dr.	SOMNATH		MUKHERJEE	KALPANA CHAWLA CENTER FOR SPACE AND NANO SCIENCES.	We obtain a scaling relation for spherically symmetric k-essence scalar fields φ(r, t) for an inhomogeneous cosmology with the Lemaitre-Tolman-Bondi (LTB) metric. We show that this scaling relation reduces to the known relation for a homogeneous cosmology when the LTB metric reduces to the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric under certain identifications of the metric functions. A k-essence lagrangian is set up and the Euler-Lagrangian equations solved assuming φ(r, t) =φ 1 (r) + φ 2 (t). The solutions enable the LBT metric functions to be related to the fields. The LTB inhomogeneous universe exhibits late tim accelerated expansion i.e.cosmic acceleration driven by negative pressure.
Mr.	Anik		Rudra	HNB Garhwal University (A Central University), Uttarakhand, India	The energy extraction mechanism via the Penrose process and superradiant modes and the gravitational particle collisions around a rotating dyonic black hole (BH) in N=2, U(1)^2 gauged supergravity model have been extensively studied. Interestingly, our result indicates that for a strongly coupled extremal black hole under certain constraint the maximum efficiency for this case becomes almost double while compared with the case of extremal Kerr black hole spacetime in general relativity (GR). Under the same constraint, the maximum amount can be extracted from an extreme black hole which increases with respect to the coupling constant and comes to have an upper bound which is ∼60.75% of its total energy. We provide an upper limit on the gauge coupling constant up to which the phenomenon of Superradiance is likely to occur. For the extremal spacetime, an infinitely large amount of center-of-mass energy (CM) can be achieved closer to the horizon which allows the BHs emerging in supergravity scenario to serve as an influential supercollider ever as compared to Kerr and any other generalized Kerr black hole explored so far in GR and in other alternative theories of gravity. Therefore, can be envisaged to open up a new window of understanding physics at the Planck energy scale. However, the CM energy for the nonextremal spacetime is however shown to be finite.
Dr.	Sunil	Kumar	Tripathy	Indira Gandhi Institute of Technology, Sarang	Cosmic Transit behaviour with a hybrid scale factor
Mr.	SOUMENDRA	KISHORE	ROY	Presidency University Kolkata	Title: Kinematics of Two-particle Scattering in Black Hole Backgrounds\nAbstract: We show that particle scattering in general curved backgrounds entails {it six} independent, kinematical Mandelstam-like invariants, instead of the two in flat spacetime. Spacetime isometries are shown to lead to constraints between these parameters, so that for standard black holes like Schwarzschild, Reissner-Nordström or Kerr spacetimes, the number of {it independent} parameters may be less than six. We compute the values of these independent parameters very close to the event horizon of the black holes. We demonstrate the existence of kinematical domains in the parameter space of particle trajectories for which some of the independent invariants may become unbounded above, as the point of collision approaches the event horizon. For particle scattering, this would imply the possibility of scattering with very large center-of-mass energy-squared and/or very large momentum-transferred-squared, making this astrophysically a laboratory for physics beyond the standard model. (arXiv:1905.09089 [gr-qc])
Mr.	Rittick		Roy	Indian Institute of Technology Mumbai	Kerr black holes coupled to quantized bosonic fields display a special version of the Hawking effect, governed by the superradiance condition. This leads to rapid growth of boson cloud through spontaneous creation, leading to slowing down of the black hole, and detectable as growth of the black hole shadow. This can be developed into a technique for searching or constraining the existence of ultralight bosons. We study this phenomenon in the shadow of a black hole and put estimates on the evolution time scales and subsequent change in the black hole shadow diameter. Our study shows that these evolutions take place over observable time scales for black holes of mass M_x000C_sun − 10^6 Msun_x000C_.\nWe also study the specific case of SgrA∗, in detail, and show that with current shadow imaging technique this might be the only candidate for observation of such signals.
Mr.	Arindam	kumar	chatterjee	West Bengal State University	The purpose of this study is the derivation of the equation of motion for particles and light in the spacetime of Reissner-Nordström-(anti-)de Sitter black holes in the background of different kinds of regular and exotic matter fields. The complete analytical solutions of the geodesic equations are given in terms of the elliptic Weierstraß ℘-function and the hyperelliptic Kleinian σ-function. Finally after analyzing the geodesic motion of test particles and light using parametric diagrams and effective potentials, we present a list of all possible orbits.
Prof.	Subodha		Mishra	Department of Physics, Siksha ’O’ Anusandhan Deemed to be University, Bhubaneswar-751030, India	Title: RELATIVIZED NEWTONIAN QUANTUM GRAVITY : A RELATION CONNECTING TIME, TEMPERATURE AND COSMOLOGICAL CONSTANT . Abs: We establish a theory of quantum gravity which is formulated [1] after we special relativize the quantized Newton-Cartan-Schrodinger theory [2]. The N-C theory is the true Newtonian limit of the General Theory of Relativity (GTR). It is known that GTR can not be covariantly quantized. So we take a detour to reach at the Quantum Theory of Gravity. Since the relativization is done after we quantize the N-C-S theory, we call it an effective theory. Also, since gravity is the dominant interaction at large scales, quantum cosmology should be based on the theory of quantum gravity and rightly we derive a relation connecting time, temperature and cosmological constant [2]. Gamow's relation between time and temperature is a special case of ours when cosmological constant is exactly zero. The calculated value of cosmological constant is in very good agreement with the value known otherwise. This theory of quantum gravity not only takes into account the consistent quantization of gravity but also explains properties of our Universe and other self-gravitating[3] objects successfully.
Ms.	Baljeet	Kaur	Lotte	Department of Physics, Siksha ’O’ Anusandhan Deemed to be University, Bhubaneswar-751030, India	EXACT ENERGY OF A SELF-GRAVITATING SYSTEM : APPLICATION OF RELATIVISED NEWTONIAN QUANTUM GRAVITY\n\nBaljeet Kaur Lotte & Subodha Mishra\n\nDepartment of Physics, Siksha ’O’ Anusandhan Deemed to be University, Bhubaneswar-751030, India\n\n\n\n ABSTRACT\n\n A degenerate system of N-self-gravitating fermions, when undergoes gravitational collapse, can form a Schwarzschild black hole. By using a quantum mechanical approach for a system of self gravitating particles and choosing a single particle trial density in the Thomas-Fermi approach we calculate the ground state energy for the system of fermions [1]. We derive the Schwarzschild radius and Hawking temperature for the black hole by special relativising Newtonian quantum gravity [2]. Incorporating the exchange correlation term we find some small corrections to the above two quantities. Taking the cue from approximate ground state energy and the numerical coefficient of the Hawking temperature we derive the exact ground state energy of a system of N self-gravitating fermions which obeys the upper and lower bounds derived by other researchers long back[3]. This result can not be derived using General Theory of Relativity. Hence we establish that the relativised Newtonian quantum gravity plays a vital role in deriving certain relations where in addition to the gravitational interaction, the particulate and fermionic nature of the interacting particles are manifestly important .\n\n\nREFERENCES:\n1. S. Mishra and B. K. Lotte. Mod. Phys. Lett. A 33,1850178 (2018).\n2. S. Mishra and J. Christian, Effective theory of quantum gravity, Abramis, UK,\n (2011).\n3. J. M. Levy-Leblond, J. Math. Phys. 10, 806 (1969).
Mr.	Karim	Amir	Mosani	BITS Pilani	End state of gravitational collapse of a perfect fluid, satisfying at least the weak energy condition, is investigated. The collapsing cloud is not restricted to follow any Equation of State (EoS). Since considering arbitrary pressure in the collapsing cloud to study its end state is difficult to tackle, because it requires us to have the information about the dynamics of collapse, which is not known in a general scenario, we give a small perturbation to the mass profile corresponding to inhomogeneous dust collapse, which in turns provides a small pressure perturbation to the otherwise pressureless fluid. Two types of perturbation, we call them Type 1 and Type 2, are considered. The dependence of nakedness or otherwise of the singularity on the initial condition, in presence and in absence of perturbation, has been depicted numerically.
Ms.	P.C		LALREMRUATI	GAUHATI UNIVERSITY	Test of general relativity near Sgr A* through compact orbits of S-stars\n P.C Lalremruati1,2 ,Sanjeev Kalita1,3\n 1Department of Physics,Gauhati University,Guwahati-781014,Assam\n 2email: pcremruati905@gmail.com\n 3email: sanjeevkalita1@ymail.com\n \n\n ABSTRACT\n\nGeneral Relativity remains largely untested at strong field regimes.Astronomical tests near the supermassive black hole of the Galactic Centre(Sgr A*) have recently appeared.In this work we have calculated general relativistic periastron shift of compact orbits of S-stars near Sgr A* up to the innermost circular orbit (ISCO) while respecting “no-hairâ€
Mr.	Chiranjeeb		Singha	IISER Kolkata	In order to achieve a Hamiltonian-based canonical derivation \n of the Hawking effect, one usually faces multiple hurdles. Firstly, the spacetime foliation using Schwarzschild time does not lead to hyper-surfaces which are always spacelike. Secondly, the null coordinates which are frequently used in covariant approach, do not lead to a true matter Hamiltonian. We have introduced a new set of near-null coordinates which allows one to perform an exact canonical derivation of Hawking effect. However, there too one faces the difficulty of having to deal with non-vanishing matter diffeomorphism generator as the spatial decomposition involves a non-zero shift vector. \nThen we have introduced a new set of coordinates which allows one to perform an exact canonical derivation of the Hawking effect without having to deal with matter diffeomorphism generator.
Mr.	Mostafizur		Rahman	Jamia Millia Islamia	Strong cosmic censorship conjecture has been one of the most important leap of faith in the context of general relativity, providing assurance in the deterministic nature of the associated field equations. Though it holds well for asymptotically flat spacetimes, a potential failure of the strong cosmic censorship conjecture might arise for spacetimes inheriting Cauchy horizon along with a positive cosmological constant. We have explicitly demonstrated that violation of the censorship conjecture holds true in the presence of a Maxwell field even when higher spacetime dimensions are invoked. In particular, for a higher dimensional Reissner-Nordström-de Sitter black hole the violation of cosmic censorship conjecture is at a larger scale compared to the four dimensional one, for certain choices of the cosmological constant. On the other hand, for a brane world black hole, the effect of extra dimension is to make the violation of cosmic censorship conjecture weaker. For rotating black holes, intriguingly, the cosmic censorship conjecture is always respected even in presence of higher dimensions. A similar scenario is also observed for a rotating black hole on the brane.
Ms.	DHANYA		MENON	IISER PUNE	Numerical studies show that Anti de sitter (AdS) spacetime is nonlinearly unstable for arbitrarily small perturbations. We consider gravitational waves in confined geometry, specifically gravitational perturbations of Minkowski spacetime in (n+2) dimensions with n>=2 in presence of a Dirichlet wall. This mimics AdS boundary conditions. By decomposing metric perturbations into various spherical harmonics, one can get simplified non-homogeneous equations at arbitrary order. Results from nonlinear dynamics are applied to comment about the nonlinear stability of this system.
Ms.	Poulami		Dutta Roy	IIT Kharagpur	We obtain scalar quasi-normal modes (QNMs) in a two parameter (metric parameter 'n' and throat radius 'b_0') family of ultra-static Lorentzian wormholes proposed many years ago [1], as a generalization of the well-known Ellis--Bronnikov spacetime. It is possible to generate distinct wormhole shapes by changing the value of 'n' (the case 'n=2' is that of Ellis--Bronnikov geometry). The effective potential in the radial part of the Klein-Gordon equation shows distinct double barrier features for all n >2 geometries, for small values of 'm', the angular momentum parameter. For higher 'm' values we have a single peak effective potential irrespective of the geometry. The QNMs are numerically calculated using (i) direct integration and (ii) Prony fitting (using the time-domain profiles) [2]. Semi-analytical results are also found via a WKB analysis [2]. We discuss the suitability of each method for different members of the wormhole family by comparing the QNMs obtained using the different methods. We note that the shape of the wormhole can be clearly discerned from the corresponding QNM values for small 'n'. For higher 'n' the geometries become nearly identical and are difficult to identify from QNMs alone [2]. References: [1] S. Kar, S. Minwalla, D. Mishra and D. Sahdev, Phys. Rev. D 51, 1632 (1995). [2] P. Dutta Roy, S. Aneesh and S. Kar, to be submitted.
Dr.	Deepak		Vaid	National Institute of Technology Karnataka	The question of the origin time’s arrow is a major outstanding problem in physics. Here we present a possible mechanism for generation of a cosmological arrow via spontaneous symmetry breaking in a theory of quantum gravity. In arXiv:1401.3736, Chen and Vishwanath have shown that a local notion of time-reversal symmetry can be encoded into a gauge field living on a tensor network. Using the fact that tensor networks can be used to describe the state space of Loop Quantum Gravity (arXiv:1309.6282, arXiv:1610.02134) we show that a spontaneous symmetry breaking mechanism operating on such tensor networks can lead to the spontaneous generation of an arrow of time corresponding to the generation of non-zero order parameter for the Chen-Vishwanath gauge field.
Mr.	jebin		larosh	Graduate student, Manonmaniam Sundaranar University	\ Non- Abelian Stokes equation in Branes \"\n The surface of the branes in scalar field in 5D bulk with its dynamics and boundary conditions are derived as well with Z_3 symmetry"
Mr.	Noel	Jonathan	Jobu	Manipal Centre for Natural Sciences, Manipal Academy of Higher Education	Title: Constraints on scalar field theory including\ngravitational interaction in general D-dimension\n\nAuthors: Noel Jonathan Jobu, Dr Kazuyuki Furuuchi\n\nA choice of signs of coefficients of the higher derivative interactions can lead to a violation of causality in effective field theories. Such choice of coefficients are also inconsistent with some schemes of UV completion with respect to analyticity and unitarity. Such conditions are a part of the swampland program\ngiving us constraints on effective field theories consistent with UV completion. In this work, we explore the constraints from causality, analyticity and unitarity on scalar field theory in D-dimensions. We further study the constraints from\nimposing causality, analyticity and unitarity when gravitational interaction is included in effective field theories.
Dr.	Uma		Papnoi	D S Kothari Post Doctoral Fellow	In higher dimensions, the black holes (BHs) have exotic shapes and unusual dynamics in comparison to a four dimensional BH in general relativity (GR) and/or in other alterna-tive theories of gravity. The Myers Perry (MP) BH is a higher dimensional generaliza-tion of the asymptotically flat rotating BH in GR, i.e., the Kerr BH. We study the shadows of such five dimensional (5D) MPBH spacetime which is mainly characterized by two spin parameters namely ‘a’ and ‘b’. We have considered the case of equal spin parame-ters in equatorial plane and the radial motion of the photons to visualize the shape of the shadows for 5D MPBH in plasma background is studied in detail. The influence of plasma along with other parameters on shadow cast by a 5D MPBH spacetime is ana-lyzed and the results obtained are also compared with those of the Kerr BH case in usu-al GR.
Mr.	Vishnu		Rajagopal	University of Hyderabad	Non-commutativity and Maximal acceleration. In this work we show that the non-commutativity induces a cut-off on proper acceleration. Here\nwe use κ-deformed Minkowski space-time to get the maximal proper acceleration. Further we obtain\nthe κ-deformed Schwarzschild metric (which contain maximal proper acceleration term) and derive\nthe κ-deformed geodesic equation, valid upto first order in deformation paramter.
Mr.	Prateek		Sharma	Department of Physics, Gurukula Kangri Vishwavidyalaya, Haridwar	Null Geodesic Around a Schwarzschild Like Black Hole\n\nVarious observations have confirmed that the accelerated expansion of universe, can be explained by the mysterious presence of dark energy in our universe. There are various candidates to represent dark energy (viz. quintessence, K-essence, cosmological constant etc.). Further a generalized Chaplygin gas (GCG) model is suggested as an alternative to quintessence mimicking the acceleration of the universe through an exotic equation of state. We study the null geodesic around a Schwarzschild black hole (BH) in a GCG scenario and compare it with a pure Schwarzschild BH case in usual general relativity (GR) in prescribed limits. The study of various aspect of gravitational lensing in such GCG model is currently being carried out to understand the effect of dark energy even at small scales.
Mr.	Gera		Suvikranth	IIT KHARAGPUR	Title: Taming Timelike Curves and Dirac strings. Abs: The solutions to Einsteins theory of General Relativity have inherent pathologies in the form of Curvature singularities and Timelike curves. In this paper we address the problem of closed timelike curves and Dirac strings in vaccum gravity. We introduce and establish a method to eliminate these problems in the context of Taub-NUT and miser space time, which are superceded by smooth solutions of first order field equations. For the case of Taub-NUT the resulting spacetime is a unique degenerate extension. The proposed framework has an inherent geometric interpretation of magnetic charge in the absence of matter.
Ms.	Rajani		K.V	National Institute of Technology Karnataka, Surathkal.	We study the thermodynamics and phase transition of regular Bardeen AdS black hole in the extended phase space, where the cosmological constant is taken as thermodynamic pressure. Using isotherms, T-S plot and specific heat studies a first order phase transition is observed. The thermodynamic study is followed by the construction of a heat engine using the black hole as working substance. The efficiency of the heat engine is calculated via a thermodynamic cycle in the P-V plane, which absorb and eject heat. By adding quintessence dark energy parameter a significant improvement in efficiency is achieved.
Mr.	Naveena		Kumara A.	National Institute of Technology Karnataka, Surathkal	Title: Microscopic structure of RN AdS blackhole in an alternate approach.\n\nAbstract: The microscopic structure of the charged AdS blackhole is studied using Ruppeiner geometry in alternate phase space. The alternate phase space is constructed by identifying the square of the charge of the blackhole with the thermodynamic variable pressure. We calculate the Ruppeiner invariant scalar R along the coexistence curve to study the interaction between the blackhole constituents. In this treatment the sign of the curvature scalar indicates the type of the statistical interaction. \n\nIn this work we probe the role of global monopole in the statistical interaction of the blackhole. In the alternate phase space the interaction is always repulsive since R is positive for both small blackhole (SBH) and large blackhole (LBH) phases. The phase transition from SBH to LBH can be interpreted as the continuous expansion due to the degenerate pressure in the interior of SBH. The presence of monopole parameter enhances this behavior to a large extent.
Mr.	AHMED		RIZWAN C.L	National Institute of Technology Karnataka, Surathkal	Title: Phase transition in AdS blackhole via alternate phase space\n\nAbstract: We investigate the phase transitions in AdS blackhole via an alternate approach. In this method the square of the charge is taken as an independent thermodynamic variable. This treatment differ from the conventional approach where an extended phase space is constructed with cosmological constant as fluid pressure. In the alternate phase space charged AdS blackhole shows van der Waals like behavior as in extended phase space.\n\nIn our study we have considered an RN AdS black hole with a global monopole. The effect of the global symmetry breaking parameter is observed in thermodynamics. The isotherms in alternate space, Gibbs free energy and coexistence curve are affected by this parameter. The increasing strength of global monopole suppresses van der Waals like behavior. The advantage of alternate approach is that the phase transition of the blackhole can be attributed to its charge, which is physically eminent.
Mr.	Joydeep		Chakravarty	ICTS-TIFR Bangalore	We study the \Bags of gold\" paradox for a Schwarzchild black hole in an asymptotically $AdS$ spacetime. The paradox states that naively one can construct configurations in $AdS$ such that their entropy exceeds the Bekenstein-Hawking bound. We conjecture that the resolution of the paradox is due to the fact that the bulk degrees of freedom are overcounted in the context of semiclassical gravity in $AdS$. We show that the holographic dual CFT description of the black hole has no such paradox. We motivate the conjecture by demonstrating explicit examples constructed using matrix models of the dual Yang Mills theory which correctly provide the description of these overcounted degrees of freedom in the bulk. (Additional Note: This work is done in collaboration with Suvrat Raju and is going to appear in 19XX.XXXXX.)"
Prof.	Bivudutta		Mishra	BITS-Pilani, Hyderabad Campus	Title: Phantom Cosmology in Modified Theory of Gravity\nAuthor: B. Mishra, Department of Mathematics, BITS-Pilani, Hyderabad Campus,\nHyderabad-500078, India, E-mail:bivudutta@yahoo.com\nAbstract: In this paper, we have constructed some phantom models without any Big Rip\nsingularity at finite time in the frame work of modified theory of gravity. In the geometrical\npart of the action, we have considered a coupled linear function of the Ricci Scalar and the\ntrace of the energy momentum tensor in place of the Ricci scalar. Four Little Rip and Pseudo\nRip models have been investigated where the equation of state parameter evolves\nasymptotically and sufficiently rapidly to -1. The effect of the coupling constant of the\nextended gravity theory on the dynamics has been discussed. Possible wormhole solutions for\nthe phantom models are obtained. The possibility of Big Trip in wormholes are discussed for\nthe models. We observed that, it is possible to obtain wormhole solutions in phantom models\nwhere Big Rip can be avoided. The time of Big Trip for all the rip models considered in the\nwork have been calculated. It is demonstrated that, a modified gravity theory such as the\npresent one delays the time of occurrence of Big Trip in wormholes than that in GR. In\nPseudo Rip models where the models evolve asymptotically to a de Sitter universe, Big Trip\ncan occur with certain limiting conditions for the wormhole throat. We have obtained those\nconditions for our models.\nKeywords: Modified Gravity, Little Rip, Wormhole Solutions
Mr.	Nomaan		X	Raman Research Institute	On the road to the larger goal of understanding if black hole entropy might arise from a discrete picture of spacetime, we numerically study the entanglement entropy of de Sitter (dS) horizons. Using the causal set hypothesis and Sorkin's covariant definition of entanglement entropy we show that the various horizons in 2, 4 dimensions follow the usual area law. A caveat here is the use of a double-truncation prescription and we briefly comment on its use.
Dr.	Muhammed		Amir	University of KwaZulu-Natal, Durban, South Africa	We construct theoretical investigation of the black hole shadow for rotating charged black hole in an asymptotically flat, axisymmetric, and stationary spacetime with Weyl corrections. This spacetime is characterized by mass ($M$), charge parameter ($q$), rotation parameter ($a$), and Weyl coupling constant ($alpha$). We derive photon geodesics around the black hole and compute expressions for impact parameters with the help of photon spherical orbits conditions. We show how the presence of coupling constant $alpha$ affects the shapes of black hole shadow from the usual Kerr-Newman black hole. A comparison with the standard Kerr and Kerr-Newman black hole is also included to observe the potential deviation from them. We find that the radius of black hole shadow decreases and the distortion in the shape of shadow increases with an increase in charge $q$ for both positive and negative values of coupling constant $alpha$.
Dr.	PARTHA	PRATIM	PRADHAN	H. M. M. College For Women	We investigate the energy extraction by the Penrose process in Kerr-MOG black hole~(BH). \nWe derive the gain in energy for Kerr-MOG .\nFor extremal Kerr-MOG BH, we determine the maximum gain in energy . We observe that the MOG parameter has a crucial role in the energy extraction process and it is in fact diminishes the value of ΔE in contrast with extremal Kerr BH. Moreover, we derive the emph{Wald inequality and the Bardeen-Press-Teukolsky inequality} for Kerr-MOG BH in contrast with Kerr BH. Furthermore, we describe the geodesic motion in terms of three fundamental frequencies: the Keplerian angular frequency, the radial epicyclic frequency and the vertical epicyclic frequency. These frequencies could be used as a probe of strong gravity near the black holes
Mr.	Muhammad	Sabir	Ali	Research Scholar	In this work present a study on greybody factor of a class of regular black holes in de Sitter spacetimes which includes Bardeen and Hayward regular de Sitter black holes. Greybody factor as a characteristic of effective potential barrier, will be presented. We discuss the role of cosmological constant both, in the absence as well as in the presence of non-minimal coupling. Considering non-minimal coupling as a mass term, its effect on the greybody factor will be discussed. We also elaborate the significance of the results by giving formulae of differential energy rate and general absorption cross section. The greybody factor gives insight into the spectrum of Hawking radiations.
Mr.	Wadbor		Wahlang	Indian Institute of Technology, Guwahati	Fermi arcs can be observed in the pseudogap phase of high-temperature superconductors. In\nthe present work, we used the techniques from gauge-gravity duality to model Fermi arcs.\nWe study the Fermionic system in Q-lattice background, a massive complex scalar field in the bulk is introduced to mimic the phase transition at the asymptotic boundary. From the\ntwo-point functions, we observed an anisotropic gap in the spectral function which appears to be the arc-like contour of a Fermi surface.
Mr.	Surojit		Dalui	Indian Institute of Technology Guwahati	Phenomenology near black hole is very important to shed light in\ndifferent aspects of black hole. Community is exploring the area at astrophysical and quantum scales. One main concern is to quantify particle dynamics as it approaches towards horizon. Here we have analyzed the motion of a massless and chargeless particle very near to the event horizon. It reveals that the radial motion has exponential growing nature which indicates that there is a possibility of inducing chaos in the particle motion of an integrable system when it comes under the influence of\nthe horizon. This is being confirmed by investigating the Poincaré section of the trajectories with the introduction of a harmonic trap to confine the particle’s motion. Two situations are investigated: (a) any static, spherically symmetric black hole and, (b) spacetime represents a stationary, axisymetric black hole (e.g., Kerr metric). In both cases, the largest Lyapunov exponent has upper bound which is the surface gravity of the horizon. We find that the inclusion of rotation in the spacetime introduces\nmore chaotic fluctuations in the system. Our results based on the general relativity are quite robust. The present results are quite general and may be of interest for the researchers working in other areas.
Mr.	Sumit		Dey	Indian Institute of Technology, Guwahati	The incompressible Navier-Stokes equation is known to govern the hydrodynamic limit of essentially any fluid and its rich non-linear structure has critical implications in both mathematics and physics. The employability of the methods of Riemannian\ngeometry to the study of hydrodynamical flows has been previously explored from a purely mathematical perspective. We propose a bulk metric in (p+2)-dimensions with the construction being such that the induced metric is flat on a timelike r = r_ c (constant) slice. We then show that the equations of parallel transport for an appropriately defined bulk velocity vector field along its own direction on this manifold when projected onto the\nflat timelike hypersurface requires the satisfaction of the incompressible NS equation in (p + 1)-dimensions. Additionally, the incompressibility condition of the fluid arises from a vanishing expansion parameter θ, which is known to govern the convergence (or divergence) of a congruence of arbitrary timelike curves on a given manifold. In this approach Einstein’s\nequations do not play any role and this can be regarded as an off-shell description of fluid-gravity correspondence. We argue that our metric effectively encapsulates the information\nof forcing terms in the governing equations as if a free fluid is parallel transported on this curved background. We finally discuss the implications of this interesting observation and its potentiality in helping us to understand hydrodynamical flows in a probable new setting.
Dr.	Satish Kumar		Saravanan	International Institute of Physics, Brazil	Title: Influence of spin in curved geometries. \nAbstract: We present the analytical description of gravitational two-body problem in the spinning particle limit. Recently developed equations of motion and world-line perturbation theory for particles carrying spin are reviewed. Exact circular orbit solutions, eccentric-planar orbits and the innermost stable circular orbit are found in the Kerr spacetime. Non-planar eccentric orbits including the precessional frequency of the plane are predicted in Schwarzschild spacetime. Entire calculations are performed with complete spin of the particle and in a fully relativistic way.
Ms.	RENU		DHAYAL	Student	A minimally coupled nonclassical inflaton (homogeneous scalar field) is analyzed in the semiclassical theory of gravity in the flat Friedmann-Robertson-Walker (FRW) universe. By use of thermal squeezed vacuum state, we analyzed the validity of semiclassical theory by calculating density fluctuations in the oscillatory phase of the inflaton. Semiclassical theory may not be valid in the thermal vacuum state because of density fluctuations very large for squeezing parameter more than unity, however, the theory holds when the related squeezing parameter is much less than the unity. The present study is for density fluctuations due to the thermal and quantum effects using the operator method in the semiclassical theory of gravity.		Shifted to Workshop 3
Mr.	Swagat	Saurav	Mishra	Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune	Scalar perturbations during inflation can be substantially amplified by tiny features in the inflaton potential. These features look like bumps/wiggles and behave like `speed-breakers' since they lower the velocity of the scalar field as it rolls down its potential. The amplification factor of primordial fluctuations can be as large as $10^6$ and gives rise to a significant primordial black hole (PBH) density today, $\Omega_{\rm BH} \sim O(1)$. This new mechanism for PBH formation is adapted to several popular inflationary scenarios. We show that the presence of a perturbatively small speed-breaker leads to a spike in the perturbation spectrum and to an enhanced probability of BH formation in these models. We conclude that primordial black holes in several important mass ranges can easily form in single field inflationary models in the presence of small speed-breakers in the potential.		Shifted to Workshop 3
Ms.	MEGHNA		RATHORE	Ph.D. Research Scholar	We examine the validity of semiclassical theory of gravity in two-mode squeezed vacuum state in a chaotic inflationary model. The back-reaction of a quantised matter field on a classical metric is formulated in terms of semiclassical Einstein equation, which has the expectation value in some quantum state of the stress tensor as a matter source. This theory is a good approximation only when the fluctuations around the expectation value of the stress tensor of the matter fields are small. We calculate a dimensionless parameter suggested by Kuo and Ford as a natural measure of the strength of fluctuations. Based on the above criterion fluctuations for a inflaton on a flat background metric in oscillatory regime of inflaton in the two-mode squeezed vacuum state was evaluated. It was found that fluctuation in the energy-momentum tensor depends on the associated squeezing parameter for the state considered, thereby putting limits on the validity of semiclassical approximation.		Shifted to Workshop 3