| Talks Selected for Workshop -3 | ||||||||||||
| Title | First name | Last name | Affiliation | Abstract | ||||||||
| Prof. | CS | Unnikrishnan | Tata Institute of Fundamental Research | Title: Gravity, Quantum State Reduction, and The Quantum Measurement Problem: New Results and Predictions Abstract : The Quantum Measurement Problem (QMP) is one of the foremost unsolved problem in fundamental physics. This problem and its ultimate resolution is intimately related to the understanding of the wavefunction, its superposition, evolution, and collapse, as well as the separation of entanglement during observations. With the macroscopic apparatus and the observer involved in the observations, the question arises whether there is a quantum-classical transition zone, from the microscopic to the macroscopic world. The possible role of gravity in the resolution of the QMP has been speculated in different contexts. Many experiments are active to probe the speculations of spontaneous quantum state reduction and a mesoscopic scale for the and quantum-classical transition. I discuss a new results obtained from a reconstruction of Hamiltonian action mechanics that directly impacts these speculations. I will discuss the reasons for absence of a scale of mass or size of transition to classicality of quantum phenomena and definite predictions of null results for representative experiments. I will show why the superposition of long range gravitational fields are excluded in the conventional quantum superposition of different mass states, as in the case of neutrinos. This has consequences in the conceptual formulation of quantum gravity. Finally, I will discuss a solution of the quantum measurement problem, sans gravity or spontaneous reduction, that is already in complete consistency with all empirical evidence. References: C. S. Unnikrishnan, Reconstructing Quantum Mechanics Without Foundational Problems, arxiv:1812.06088. | ||||||||
| Dr. | Sayantan | Choudhury | Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Potsdam. | Title: Open Quantum Theory of Two entangled atoms in De Sitter Space\nAbstract:\n In this work, 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. Here we have explicitly computed the many-body (two atomic) thermal Wightman functions by applying Schwinger-Keyldish techniques along with the well known Kubo-Martin-Schwinger (KMS) conditions. 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. Additionally, we also analytically solve the time evolution of the reduced density matrix of the system in the presence of effective Hamiltonian and quantum dissipator or Lindbladian to explicitly know about the time evolution of the system and also the large-time equilibrium behaviour of the OQS under consideration, which will help us to know about the equilibrium temperature dependence of the environment (thermal bath) of OQS. Finally, we quantify various quantum information theoretic measure to study the effect of quantum correlations of the OQS. | ||||||||
| Dr. | Abhirup | Ghosh | Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Potsdam-Golm | One of the consequences of the black-hole “no-hair†theorem in general relativity (GR) is that gravitational radiation (quasinormal modes) from a perturbed Kerr black hole is uniquely determined by its mass and spin. Thus, the spectrum of quasinormal mode frequencies have to be all consistent with the same value of the mass and spin. Similarly, the gravitational radiation from a coalescing binary black hole system is uniquely determined by a small number of parameters (masses and spins of the black holes and orbital parameters). Thus, consistency between different spherical harmonic modes of the radiation is a powerful test that the observed system is a binary black hole predicted by GR. We have formulated such a test, developed a Bayesian implementation, demonstrated its performance on simulated data, and investigated the possibility of performing such a test using previous and upcoming gravitational wave observations [Phys. Rev. D 99, 104056]. We have further shown, given a sufficiently loud signal, how this test is indeed able to distinguish a binary black hole coalescence, from the coalescence of two compact objects, where at least one of the compact objects have a multipolar structure different from a black hole. | ||||||||
| Prof. | SARBARI | GUHA | Department of Physics, St. Xavier | In this paper we have examined the validity of the generalized second law of thermodynamics (GSLT) in an expanding FRW universe filled with different variants of Chaplygin gases. Assuming that the universe is a closed system bounded by the cosmological horizon, we first present the general prescription for the rate of change of total entropy on the boundary surface. In the subsequent part we have analyzed the validity of the generalised second law of thermodynamics on the cosmological apparent horizon and the cosmological event horizon for different Chaplygin gas models of the universe. The analysis is supported with the help of suitable graphs to clarify the status of the GSLT on the cosmological horizons. We have found that the validity of GSLT on the cosmological event horizon of these models depend on the choice of free parameters in the respective models. [arXiv:1901.10814v2] | ||||||||
| Dr. | Apratim | Ganguly | ICTS-IFR | In this talk, we will discuss virial relation in a wide class of extended theories of gravity | ||||||||
| Dr. | sanjeev | sanjeev | kalita | Gauhati University | On new gravitational physics near the Galactic Center black hole\n\nSanjeev Kalita1,2\n1Department of Physics, Gauhati University, Guwahati-781014, Assam.\n2e-mail: sanjeev@gauhati.ac.in\n\n \n\nAbstract\nTests of general relativity and its alternatives are crucial for understanding fundamental problems of the theory and cosmology. The Supermassive Black Hole of the Galactic Center (Sgr A*) provides an ideal laboratory for astronomical tests of new gravitational physics. This work reports that power law gravity f(R) ~ R^n appearing out of curvature correction to quantum vacuum fluctuations naturally yields a Yukawa type scalar fifth force with potential exp(-M_{psi}r)/r , where M_{psi} is the mass of the f(R) scalarons. The relation between scalaron field Psi=df(R)/dR and momenta (k) of gravitationally corrected vacuum fluctuations and the same between the scalaron mass and fluctuation momenta (k) have been deduced. The scalaron mass comes out in the range M_{psi}=10^{-18} - 10^{-21} eV presenting scale lengths of the fifth force lambda= 100 -1000 au. The Yukawa correction to Newtonian potential is shown to be a quantum gravity correction to the smooth Schwarzschild metric. The Yukawa coupling strength (alpha) in the corrected Newtonian potential is connected to the background scalaron field amplitude, (Psi_{0}) . The ratio of periastron shift of the S-stars near Sgr A* in presence of scalaron fifth force to that in GR has been expressed in terms of quantum gravity fluctuation parameters Psi_{0} and lambda (=1/k_{min}) with k_{min} being the infrared cut off of the fluctuations. This has been studied with respect to orbital size (a) in the range a = (100 - 8000) au and being parameterized by the background field amplitude and range of the fifth force. Also the effect has been studied with respect to variation of the field amplitude in the range Psi_{0}=10-1000 (coupling alpha = 0.01 - 0.0001 ) through parameterization with the pair (lambda, a ). For both of the cases,lambda<a and lambda>a , it has been found that scalaron fifth force affects the orbital precession in larger orbital size. The periastron shift with scalaron is found to be between 0.1% and 14% of the GR value. This is a new and independent effort to see the quantum gravitational actions in the classical regions surrounding the black hole through infrared mode of vacuum fluctuation. It is inferred that the scalaron fifth force demands not only new tests of gravitational physics (including scalar hair and scalar dark matter) but also challenging precision of upcoming astrometric facilities of the Extremely Large Telescopes to be dedicated for understanding gravity. \n\nKey words: black hole - fifth force -quantum gravity -Galaxy: center | |||||||
| Dr. | Seema | Satin | IISER Pune | A correspondence between fluctuations of minimally coupled scalar fields and that of an effective perfect fluid is shown to exist. A similar correspondence between the stress tensors themselves is known and widely used in literature.Using recent results obtained in semiclassical stochastic gravity for the\n fluctuations of the quantum stress tensor, a new correspondence is obtained, which is argued to be of fundamental importance to statistical analysis of\n systems in curved spacetime. It is shown that the scalar field fluctuations are related to covariances of energy density and pressures of the effective perfect fluid. Such a correspondence between the semiclassical and classical fluctuations therefore, is expected to give insight to the mesoscopic phenomena for gravitating systems and would further enhance the perturbative\n analysis for cosmological spacetimes and astrophysical objects in the decoherence limit. A kinetic theory in curved spacetime may find useful insights from such correspondences in future work. | ||||||||
| Dr. | Soumya | Jana | University of Geneva | Title: Overcharging the extremal Born-Infeld black holes and the cosmic censorship. Abstract: We have studied the gadenken experiment of overcharging the extremal black holes in Eddington-inspired Born-Infeld (EiBI) gravity. The EiBI gravity is modification to general relativity (GR) inspired by the nonlinear Born-Infeld electrodynamics. The overcharging problem in GR can be described as whether an initial extremal or near-extremal Reissner-Nordstrom black hole can turn into a naked singularity by absorbing an incoming charged test particle. Its importance lies in the question of validity of cosmic censorship conjecture which tells us that spacetime singularity always be covered by horizon. We have showed that unlike GR, the overcharging could be possible for a charged extremal black hole in EiBI gravity as long as the matter sector is described by usual Maxwell's electrodynamics. Once the matter sector is also the Born-Infeld type (i.e. Born-Infeld electrodynamics) the overcharging is not possible only under certain condition on the theory parameters. Ref.: S. Jana, R. Shaikh, and S. Sarkar, Phys. Rev. D 98, 124039 (2018). | ||||||||
| Prof. | Mandar | Patil | IIT Dharwad | Title: Gravitational Lensing by Binary Black Holes. \nAbstract: Binary black holes have been in limelight off late due to the detection of gravitational waves from coalescing compact binaries in the events such as GW150914. In wake of this we study gravitational lensing by the binary black holes modeled as equal mass Majumdar-Papapetrou dihole metric and show that this system displays features that are quite unprecedented and absent in any other lensing configuration investigated so far. We unravel the existence of a new set of relativistic images and caustics. We also discuss the implication of our study for gravitational wave science. (Based on Phys. Rev. D 95, 024026 (2017)) | ||||||||
| Dr. | Suman | Ghosh | Indira Gandhi National Tribal University | We discuss particle production by scalar and spin 1/2 fields in a cosmological braneworld back ground. The renormalized energy-momentum tensor has been derived using the adaibatic regularization method. Our results show the effect of warping on the localization of matter that is created as a quantum consequence of the evolution of bulk. | ||||||||
| Mr. | Karthik | Rajeev | PhD Student | In flat spacetime, two inequivalent vacuum states which arise rather naturally are the Rindler vacuum (R) and the Minkowski vacuum (M). We discuss several aspects of the Rindler vacuum, concentrating on the propagator and Schwinger (heat) kernel defined using R, both in the Lorentzian and Euclidean sectors. We start by exploring an intriguing result due to Candelas and Raine, viz., that G_R, the Feynman propagator corresponding to R, can be expressed as a curious integral transform of G_M, the Feynman propagator in M. We show that, this relation actually follows from the well-known result that, G_M can be written as a periodic sum of G_R, in the Rindler time, with the period 2πi. We further show that the integral transform result holds for a wide class of pairs of bi-scalars (FM,F_R), provided F_M can be represented as a periodic sum of F_R with period 2πi. We provide an explicit procedure to retrieve F_R from its periodic sum F_M, for a wide class of functions. An example of particular interest is the pair of Schwinger kernels (K_M,K_R), corresponding to the Minkowski and the Rindler vacua. We obtain an explicit expression for K_R and clarify several conceptual and technical issues related to these biscalars both in the Euclidean and Lorentzian sector. In particular, we address the issue of retrieving the information contained in all the four wedges of the Rindler frame in the Lorentzian sector, starting from the Euclidean Rindler (polar) coordinates. This is possible but requires four different types of analytic continuations, based on one unifying principle. Our procedure allows generalisation of these results to any (bifurcate Killing) horizon in curved spacetime. | ||||||||
| Ms. | Isha | Kotecha | Albert Einstein Institute - Potsdam | Title: Towards a thermal discrete quantum spacetime.\n\nAbstract: The intersection of thermodynamics, quantum theory and gravity has revealed many profound insights, while also posing new questions. Here, we present a tentative generalisation of equilibrium statistical mechanics and thermodynamics potentially compatible with a key feature of general relativity, background independence. We emphasise on an information-theoretic characterisation for generalised Gibbs states, based on a principle of maximum entropy that is shown to be particularly valuable in the absence of absolute notions of energy and time. Based on this, we outline a framework for statistical mechanics of combinatorial and algebraic quantum gravity degrees of freedom commonly used in discrete approaches like loop quantum gravity and group field theory, thus providing a preliminary formulation of a thermal discrete quantum spacetime; and apply it in concrete examples. | ||||||||
| Mr. | Indranil | Chakraborty | IIT KHARAGPUR | Title: \n Displacement and velocity memory effects in exact plane gravitational wave spacetimes.\n(Indranil Chakraborty & Sayan Kar)\nAbstract: \n We explore the recent renewed interest [1] in the behaviour of geodesics in the exact, vacuum plane gravitational wave line element (in Brinkmann coordinates ), in order to arrive at a better understanding of the well-known displacement and velocity memory effects. We note that it is possible to arrive at such memory effects using (a) the solutions of the geodesic equations directly , (b) the geodesic deviation equations or (c) the Raychaudhuri equations for geodesic congruences [2].\nThe deviation equations are first qualitatively analysed using a generic pulse profile (for the freely specifiable functions in the exact plane gravitational wave line element ) to show how memory arises. Next, we find solutions (analytic) of the geodesic equations for two different functional forms of the pulse profiles, namely, (a) a square pulse and (b) a sech-squared pulse. The reason for such choices for the profiles is largely motivated from the analytical solvability (partial) of the concerned equations.\nWe explicitly show the occurrence of both displacement and velocity memory effects through our detailed solutions for timelike geodesics. Finally, we turn to the Raychaudhuri equations to study the behaviour of the kinematic variables (expansion, shear and rotation) for timelike geodesic congruences. The nature of the line element in Brinkmann coordinates reduces the problem to an effective two dimensional one. We are able to solve for the evolution of the kinematic variables for the above-mentioned pulse profiles. The passage of the gravitational wave pulse causes an initial parallel congruence to get sheared and eventually focused. The connection between the memory effect and the rise in shear is duly noted. Possible generalisations in gyraton spacetimes are also suggested. \n\nReferences:\n[1] P.-M. Zhang, C. Duval, G. W. Gibbons and P. A. Horvathy, Phys. Rev. D 96, 064013 (2017) \n[2] I. Chakraborty and S. Kar, arXiv: 1901.11236 [gr-qc] | ||||||||
| Prof. | Sayan | Kar | Dept. of Physics and CTS, IIT Kharagpur 721302, India | Scalar quasinormal modes in a symmetric, finite triangular barrier\n\nSayan Kar and Poulami Dutta Roy \n\nDepartment of Physics, IIT Kharagpur, 721302, India\n\nAbstract\n \nScalar quasinormal modes are obtained for a finite, symmetric triangular barrier potential. The solution to the scalar wave equation (spatial part) is in terms of Airy functions which makes the triangular barrier a new member in the exclusive class of potentials for which the QNMs can be analytically found. We apply the Ferrari-Mashhoon idea to find the QNMs and find a good comparison with results obtained by direct numerical \nintegration with QNM boundary conditions. We also demonstrate how such a barrier may arise in the case of scalar wave propagation in a tailor-made wormhole spacetime. \nThe time domain profiles are obtained and they clearly depict the decaying QNM ringing of scalar perturbations in this wormhole, thereby confirming its stability. Finally, we highlight the fact that apart from pedagogic relevance, such a triangular barrier may be used to approximate any single barrier effective potential such as the one which arises for scalar wave propagation in Ellis-Bronnikov(EB) spacetime. It is observed through a comparison of QNM values, that the triangular barrier can indeed serve as a\nreasonably good approximation for the known effective potential in EB spacetime.\n\n\nReferences:\n\n1. P. Dutta Roy, J. Das and S. Kar, (to appear in EPJ Plus (2019)). | ||||||||
| Dr. | SOUMEN | MONDAL | JADAVPUR UNIVERSITY, KOLKATA | Title: The relativistic equation of states in accretion and wind flows.\nAbstract: Using this relativistic equation of state(EOS) in which the adiabatic index (ratio of specific heats) varies smoothly from 5/3 to 4/3 as a function temperature, thus on the radius, we reinvestigate the issue of the formation of the shocks in accretion and wind solutions once again. We find that except for the region very nearby the compact object, does not change significantly from its non-relativistic value and therefore the EOS mostly remains non-relativistic in nature. As a consequence the existence of two saddle type critical point becomes a rare possibility indicating that it is an artifact of the choice of the constant ultra-relativistic 4/3. Therefore, the formation of shocks in the flow (which require the presence of two saddle type points) becomes unlikely. | ||||||||
| Dr. | Srijit | Bhattacharjee | IIIT Allahabad | In this work we discuss the strong cosmic censorship conjecture for AdS black holes. We implement Ori model for charged Reissner-Nordstorm Black hole in AdS and show the inner horizon becomes unstable due to | ||||||||
| Mr. | Abhishek | Mathur | Raman Research Institute | In this talk, I will discuss an observer independent formalism developed by Sorkin and Johnston (SJ formalism) for studying quantum field theory in a bounded region of any globally hyperbolic spacetime. I will start with a general introduction to the SJ formalism followed by the results of SJ Wightman function for massless and small mass scalar field in a causal diamond of 2D Minkowski spacetime. If time permits I would also like to discuss the SJ formalism for QFT on a causal set. | ||||||||
| Mr. | Shalabh | Gautam | IUCAA | The treatment of future-null infinity has been a long standing problem in numerical relativity studies. Not only is it required to extract the Gravitational-Wave signals, but also to study a wide variety of other phenomena unambiguously. Examples include the cosmic censorship conjecture, critical collapse and the self force problem. One of the major challenges in including future null infinity in the numerical domain comes in dealing with arbitrary matter content. In this talk I will discuss an ongoing attempt to deal with massive _x000C_fields at null infinity in Minkowski spacetime. This involves studying the decay of the fields and the development of numerical methods capable of dealing with formally singular terms that appear in the field equations. | ||||||||
| Dr. | Kazuyuki | Furuuchi | Manipal Centre for Natural Sciences, Centre of Excellence, Manipal Academy of Higher Educaion | Cosmological consequences of the swampland bound on the saxion mass\n\nIt has been proposed that not all consistent-looking Effective Field Theories (EFTs) are really self-consistent if one takes into account interactions with gravity. The swampland program [Vafa 2005] is an attempt to find general enough criteria which identify such inconsistent EFTs. We studied cosmological consequences of one of the swampland criteria which puts an upper bound on the mass of the radial counterpart (saxion) of a periodically identified field (axion). From the bound on the mass of the saxion together with the observational upper bound on the non-Gaussianity in the primordial density perturbations, we obtain constraints on the parameter space of the axion-monodromy inflation models. | ||||||||
| Mr. | Sajal | Mukherjee | IUCAA, Pune. | Title : THE MOTION OF EXTENDED OBJECT IN CURVED SPACETIME. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Abstract : In this talk, I shall introduce the motion of extended objects with multipole moments occupying a finite size in space. I discuss their various interesting features along with highlighting their distinctive remarks from geodesic orbits. In particular, I shall focus on two particular events: first is the resonance phenomenon associated with the pole-dipole or spinning particle in Kerr spacetime; and second, the multipole interactions between different moments, i.e., monopole, dipole or quadrupole, of the extended test particle and central object. Several theoretical and observational implications involving extended objects will also be mentioned in brief. | ||||||||
| Prof. | SHANKARANARAYANAN | S | IIT Bombay | The near-horizon black-hole symmetries need to be incorporated in any microscopic theory of gravity. Typically such attempts focus only on the microscopic theory of the event horizon of the stationary Black Hole. We develop a microscopic model for the horizon of a Black Hole slightly away from the stationary state, the dynamics of which resembles a viscous fluid. The model incorporates $S1$ diffeomorphism, a near-horizon symmetry of the Black Hole, in terms of a Virasaro algebra. However, the model developed here is not a CFT but closely related to a particular case of the Baxter model near the critical point. We argue that the correct theory of the Horizon-fluid for a Blackhole should also be an integrable theory, which posses a representation of the Virasaro algebra. | ||||||||
| Prof. | Sandipan | Sengupta | Indian Institute of Technology Kharagpur | A dynamical formulation of vacuum gravity based on an extra dimension of vanishing proper length is introduced and explored. The most general solution of the field equations lead to an emergent Einsteinian theory associated with a stress-tensor. This is composed of a running vacuum energy, pure radiation and a vector-tensor multiplet. We demonstrate that his multiplet, which exhibits a bounded equation of state, provides a potential resolution to the `dark matter' problem. Based on these nonpropagating geometric fields, a geometric model of the galactic halo is set up. (Based on arXiv:1908.04830 [gr-qc], 2019) | ||||||||
| Dr. | Bibhas | Ranjan | Majhi | Indian Institute of Technology Guwahati | Title: Unruh effect and Fluctuation-Dissipation relation.\n\nAbstract: A uniformly accelerated (Rindler) observer will detect particles in the Minkowski vacuum, known as the Unruh effect. The spectrum is thermal and the temperature is given by that of the Killing horizon, which is proportional to the acceleration. Considering that these particles are kept in a thermal bath with this temperature, we find that the correlation function of the random force due to radiation acting on the particles, as measured by the accelerated frame, shows the fluctuation-dissipation relation. \n\nRefs. 1. Phys.Rev. D97 (2018) no.4, 045003 \n 2. arXiv:1902.03735 | |||||||
| Dr. | Mohd | Shahalam | Jamia Millia Islamia, New Delhi | We study the pre-inflationary universe for the power-law and alpha-attractor potentials, in the framework of loop quantum cosmology, in which the big bang singularity is replaced generically by a non-singular quantum bounce due to purely quantum geometric effects. The evolution can be divided into two different classes, one is dominated initially (at the quantum bounce) by the kinetic energy of the scalar field, and one is not. In both cases, we identify the physically viable initial conditions that lead to not only a slow-roll inflationary phase, but also enough e-folds to be consistent with observations. In addition, we also show that in the case when the evolution of the universe is dominated initially by the kinetic energy of the scalar field, the evolution before reheating is aways divided into three different phases: bouncing, transition and slow-roll inflation. This universal feature does not depend on the initial data of the system nor on the specific potentials of the scalar field, as long as it is dominated by the kinetic energy of the inflaton field. | Shifted to Workshop 3 | |||||||
| Mr. | Abhishek | Naskar | Indian Statistical Institute, Kolkata | Primordial Gravitational Waves (PGW) are important probe of early universe cosmology as the amplitude of two point correlation function of PGW sourced by vacuum fluctuations during inflation can tell us about the energy scale of inflation. PGW generated due to vacuum fluctuations, are highly Gaussian in nature and have very small bispectrum signal. But during inflation there can be other sources of PGW that can give rise to significant non-Gaussian signal. So alongside two point correlation function the bispectrum can also serve as an additional probe for PGW, that carries information about their origin. In this study we wanted to explore the possibility to get an enhanced bispectrum of PGW in presence of preheating particles. We analyzed the scenario using the Effective Field Theory (EFT) approach for both inflation and preheating, thereby making our analysis model independent. We are able to show that for preheating sourced PGW, large bispectrum can be generated by tuning the sound speed of tensor fluctuations and preheating particles. Expressions for model independent non-linearity parameters are calculated and we also presented the condition on the parameters such that the amplitude of bispectrum can be detectable by the upcoming surveys. | Shifted to Workshop 3 | |||||||
| Mr. | NILANJANDEV | BHAUMIK | Indian Institute of Science, Bangalore | Title: Primordial black holes dark matter from inflection point models of inflation and the effects of reheating .\n\nAbstract: We study the generation of primordial black holes (PBH) in a single field inflection point model of inflation wherein the effective potential is expanded up to the sextic order and the inversion symmetry is imposed such that only even powers are retained in the potential. By working with a quasi-inflection point, we find that PBHs can be produced in our scenario in a very relevant mass range with a nearly monochromatic mass fraction which can account for a sizeable fraction of the cold dark matter in the universe. With changing various parameters in our model, we can also generate PBHs in a higher mass range but the primordial spectrum of curvature perturbations becomes strongly tilted at the CMB scales. We also study the effects of a reheating epoch after the end of inflation on the PBH mass fraction and find that an epoch of a matter dominated reheating can shift the mass fraction to a larger mass range as well as increase their fractional contribution to the total dark matter even for the case of a monochromatic mass fraction. | Shifted to Workshop 3 | |||||||
| Dr. | Mayukh | Raj | Gangopadhyay | Centre For Theoretical Physics, Jamia Millia Islamia | We analyse the epoch of reheating after an inflationary phase in the Randal Sundrum(RS) Type-II braneworld, where we did not consider any particular model of inflation, but rather reconstructed the inflationary potential solving the flow equations using Monte Carlo (MC) approach. It is shown numerically that a potential conceived through the MC reconstruction technique can be represented by an effective potential as a function of the number of e-foldings(N). Then, the epoch of reheating is studied for this reconstructed potential. The relation between the reheating temperature and the 5-dimensional Planck mass is established. Moreover, it is argued that there is a stringent bound on the critical reheating temperature that\nalso translates to a tight bound on the brane tension. | Shifted to Workshop 3 | ||||||
| Dr. | Ratna | Koley | Presidency University | We have studied Primordial Black Holes (PBH) with emphasis on (i) their formation during inflationary phase driven by a single scalar field and (ii) their evaporation. The PBHs owe their origin to the higher peaks in the curvature power spectrum during inflation and it has been achieved successfully in multi field models but the single field models suffer from problems like entering into ultra slow roll phase etc. In this work, we have explored the possibility of having numbers of PBHs generated from high peaks, in the matter power spectrum, formed near a inflection point of the single field potential and evades the ultra slow roll issue. We further find the mass spectrum of the formed PBHs for wide range which has the capability of explaining the masses associated with merger events observed in gravitational wave experiments. Extending the mass spectrum we explore whether the PBHs could provide the required amount of dark matter and give the binding necessary for first bound structures. | Shifted to Workshop 3 | |||||||