Search

We discuss the semi-classical gravitational wave corrections to Gauss's law, and obtain an explicit solution for the electromagnetic potential. The Gravitational Wave perturbs the Coulomb potential with a function which propagates to the asymptotics., Comment: Accepted to Universe as a Communication

In this article, we investigate the interactions of a Yang-Mills (YM) wave fluctuation of a classical isotropic, homogeneous YM condensate, which models gluon plasma, with a Gravitational Wave (GW). We re-analyse the study of fluctuations of the gluon plasma using vector decomposition of the gauge field into scalar, longitudinal, and transverse modes. We find that there is an energy transfer between isotropic gluon condensate and plasmon modes, but the effect is delayed, and dependent on the initial conditions. We also studied quarks in the background of YM condensate and GW. We find that the quarks break the isotropy of the condensate and the GW couples quarks of different flavours of the SU(2) group. The GW induces flavour fluctuations, and this has interesting implications for experimental observations and quark-gluon plasma physics., Comment: 26 pages, 20 figures; Includes a discussion on motivation and implications of YM fields in the context of cosmology in the introduction and conclusion; typos corrected; Additional references included

With the discovery of gravitational waves, the search for the quantum of gravity, the graviton, is imminent. We discuss the current status of the bounds on graviton mass from experiments as well as the theoretical understanding of these particles. We provide an overview of current experiments in astrophysics such as the search for Hawking radiation in gamma-ray observations and neutrino detectors, which will also shed light on the existence of primordial black holes. Finally, the semiclassical corrections to the image of the event horizon are discussed., Comment: 25 Pages, 4 figures

In this paper, we discuss the interaction of non-Abelian SU(2) Yang-Mills progressive waves with gravitational waves. We solve and obtain some interesting solutions to pure Yang-Mills equations in different backgrounds, and perturbative solutions induced due to gravitational waves. These perturbations show `beat patterns' and depending on boundary conditions, changes in frequency. In flat space-time, when the Yang-Mills fields and the gravitational waves are in the same direction there is no interaction, unless there is self interaction of the Yang-Mills fields. In the system with non-zero self interaction the amplitudes of the perturbation are inversely proportional to the Yang-Mills coupling constant. In a cosmological background, the Yang-Mills fields and the gravitational wave interact when they are in the same direction even without self interaction of the Yang-Mills progressive fields. We find that in the electroweak symmetry broken phase of the gauge fields, the interactions are perturbative only for an infinitesimal time., Comment: 24 pages,15 figures. Accepted for publication in General Relativity and Gravitation

It is important to re-examine some of the interactions of gravitational waves with matter due to the recent discovery of the waves in LIGO. In a previous paper with Morales, interaction of gravitational waves was studied with scalar and neutrino fields in Minkowski space-time. In this paper, we find that electromagnetic waves have a similar interaction with gravitational wave in a flat background, and we comment on the implications of this for a gravitational wave detector. Primordial gravitational waves were generated in the early universe and thus it is important to study interaction of the gravitational waves in cosmological backgrounds. In this paper we discuss the interaction of electromagnetic waves and gravitational waves in a de-Sitter background. We find that the electromagnetic wave is perturbed and modulated. This result is new and will be useful in studying inhomogeneities in Cosmic Microwave Background., Comment: 16 pages, 4 figures

In this brief article we discuss the corrections to the photon orbits of a non-rotating black hole due to semiclassical fluctuations of the metric. It is found that the photon orbit impact parameter differences with the critical impact parameter become of the order of the semiclassical fluctuations. We calculate the effect of the semi-classical fluctuations on the photon orbits and show that instead of circulating the black hole infinite number of times at the critical orbit, the photons bounce off the semiclassical geometry., Comment: 22 pages, 4 figures, to appear in IJMPD

Given that gravitational waves are the future probes of the universe, it is important to test various physical effects of these on matter. This article explores the first-order perturbation, caused by a planar gravitational wave, on massless scalar and chiral fermions. We find a new propagating mode for the perturbed fields with a new dispersion relation by solving inhomogeneous differential equations. We also discuss the massive scalar field, and find interesting effects due to the gravitational wave. Our results have physical implications for early universe cosmology and also for ground-based observations, where the new mode might be able to help in the gravitational waves' detection on earth., Comment: 25 pages, 2 figures

In this paper we re-investigate the Bogoliubov transformations which relate the Minkowski inertial vacuum to the vacuum of an accelerated observer. We implement the transformation using a non-unitary operator used in formulations of irreversible systems by Prigogine. We derive a Lyapunov function which signifies an irreversible time flow. We extend the formalism to the black hole space-time which has similar near-horizon geometry of an accelerated observer, and in addition show that thermalization is due to presence of black hole and white hole regions. Finally we discuss an attempt to generalize quantum field theory for accelerated frames using this new connection to Prigogine transformations., Comment: 28 pages, two figures, clarification and references added

We re-examine vacuum polarisation of a scalar field in a quasi-local volume including the horizon. We find that Hawking radiation rate is derived as a pure decay of vacuum due to scalar field interaction with classical gravity exactly in the same way as the origin of vacuum polarisation effect in Electrodynamics., Comment: 11 pages, 2 figures

Using a new effective action predicted from quantum gravity where the sign of the Euclidean Einstein action is reversed we discuss WKB solutions in quantum cosmology and predict that this sign change might explain the origin of phantom scalars., Comment: 8 pages, Received Honourable Mention in the "Gravity Research Foundation" Essay Competition 2012

In this article we explore the origin of black hole thermodynamics using semiclassical states in loop quantum gravity. We re-examine the case of entropy using a density matrix for a coherent state and describe correlations across the horizon due to SU(2) intertwiners. We further show that Hawking radiation is a consequence of a non-Hermitian term in the evolution operator, which is necessary for entropy production or depletion at the horizon. This non-unitary evolution is also rooted in formulations of irreversible physics.

In this article a description is given of the measure in Euclidean path-integral in quantum gravity, and recent results using the Faddeev-Popov method of gauge fixing. The results suggest that the effective action is finite and positive.

A density matrix is defined using coherent states for space-times with apparent horizons. Evolving the density matrix in time gives the origin of Hawking radiation., Comment: 19 pages, 1 figure

We describe a black hole slice by a density matrix and evolve the slice in semiclassical time to search for the origin of Hawking radiation., Comment: 4 pages, Contributed talk at 12th Marcel Grossman Meeting 2009

We study semiclassical corrections to the Schwarzchild metric, and their effects on unstable orbits., Comment: 12 pages; published version

I give a resolution of the conformal mode divergence in the Euclidean gravitational path-integral by isolating the trace of the diffeomorphisms and its contribution to the Faddeev-Popov measure., Comment: 20 pgs

The entropy of apparent horizons is derived using coherent states or semiclassical states in quantum gravity. The leading term is proportional to area for large horizons, and the correction terms differ according to the details of the graph which is used to regularise the quantum gravity phase space variables., Comment: 9pgs, Talk at Theory Canada III, to appear in CJP

We calculate the exact degeneracy of states corresponding to the area operator in the framework of semiclassical loop quantum gravity, using techniques of combinatorial theory. The degeneracy counting is used to find entropy of apparent horizons derived from generalised coherent states which include a sum over graphs. The correction to the entropy is determined as exponentially decreasing in area., Comment: 29 pages, 4 figures

Coherent or semiclassical states in canonical quantum gravity describe the classical Schwarzschild space-time. By tracing over the coherent state wavefunction inside the horizon, a density matrix is derived. Bekenstein-Hawking entropy is obtained from the density matrix, modulo the Immirzi parameter. The expectation value of the area and curvature operator is evaluated in these states. The behaviour near the singularity of the curvature operator shows that the singularity is resolved. We then generalise the results to space-times with spherically symmetric apparent horizons., Comment: 52 pages, 4 figures

Using a discrete spectrum proposed for expectation values of canonical variables in black hole coherent states, the semiclassical entropy associated with the Schwarzschild space-time is derived to be the area of the apparent horizon., Comment: 7 Pages, Revtex4

We determine coherent states peaked at classical space-time of the Schwarzschild black hole in the frame-work of canonical quantisation of general relativity. The information about the horizon is naturally encoded in the phase space variables, and the perturbative quantum fluctuations around the classical geometry depend on the distance from the horizon. For small black holes, space near the vicinity of the singularity appears discrete with the singular point excluded from the spectrum., Comment: 48 pages, 18+1 figures, some modifications, references added

We discuss Wick rotations in the context of gravity, with emphasis on a non-perturbative Wick rotation proposed in hep-th/0103186 mapping real Lorentzian metrics to real Euclidean metrics in proper-time coordinates. As an application, we demonstrate how this Wick rotation leads to a correct answer for a two dimensional non-perturbative path-integral., Comment: Restructured version, 23 pages, 2 figures

We review aspects of quantisation of the 11-dimensional supermembrane world volume theory. We explicitly construct vertex operators for the massless states and study interactions of supermembranes. The open supermembrane and its vertex operators are discussed. We show how our results have direct applications to Matrix theory by appropriate regularisation of the supermembrane., Comment: 24pgs, 4 figures

We derive the vertex operators that are expected to govern the emission of the massless d=11 supermultiplet from the supermembrane in the light cone gauge. We demonstrate that they form a representation of the supersymmetry algebra and reduce to the type IIA superstring vertex operators under double dimensional reduction, as well as to the vertices of the d=11 superparticle in the point-particle limit. As a byproduct, our results can be used to derive the corresponding vertex operators for matrix theory and to describe its linear coupling to an arbitrary d=11 supergravity background. Possible applications are discussed., Comment: 22 pages, LaTeX, uses axodraw.sty; v2: minor changes, version to be published in JHEP

We study the emission rates of scalar, spinor and vector particles from a 5 dimensional black hole for arbitrary partial waves. The solution is lifted to 6 dimensions, and the near horizon $ BTZ \times S^3$ geometry of the black hole solution is probed to determine the greybody factors. We show that the exact decay rates can be reproduced from a $(1+1)$-dimensional conformal field theory which lies on the boundary of the near horizon geometry. The AdS/CFT correspondence is used to determine the dimension of the CFT operators corresponding to the bulk fields. These operators couple to plane waves incident on the CFT from infinity to produce emission in the bulk., Comment: 37 pages, minor modifications; to be published in JHEP

The emission rate of fermions from 2+1 dimensional BTZ black holes is shown to have a form which can be reproduced from a conformal field theory at finite temperature. The rate obtained for fermions is identical to the rate of non-minimally coupled fermions emitted from a five dimensional black hole, whose near horizon geometry is BTZ X M, where M is a compact manifold., Comment: 18 pages, REVTEX. Typos corrected, compact version to appear in Phys. Lett. B

We consider the gravitational scattering of point particles in four dimensions, at Planckian centre of mass energy and low momentum transfer, or the eikonal approximation. The scattering amplitude can be exactly computed by modelling point particles by very generic metrics. A class of such metrics are black hole solutions obtained from dimensional reduction of p-brane solutions with one or more Ramond-Ramond charges in string theory. At weak string coupling, such black holes are replaced by a collection of wrapped D-branes. Thus, we investigate eikonal scattering at weak coupling by modelling the point particles by wrapped D-branes and show that the amplitudes exactly match the corresponding amplitude found at strong coupling. We extend the calculation for scattering of charged particles., Comment: 16 pages, REVTEX

The semiclassical grey-body factor for massless fermion emission from the four dimensional black hole described by an ensemble of intersecting triplets of D- five-branes is shown to be consistent with the (statistical) decay rate of the branes (in the `long' D-string approximation) into massless fermionic closed string states, subject to assumptions regarding the energy distribution of colliding open string states., Comment: Some errors corrected and a reference added. 4 pages

We study the emission of scalar particles from a class of near-extremal five dimensional black holes and the corresponding D-brane configuration at high energies. We show that the distribution functions and the black hole greybody factors are modified in the high energy tail of the Hawking spectrum in such way that the emission rates exactly match. We extend the results to charged scalar emission and to four dimensions., Comment: 22 pages, REVTeX; minor typos corrected, version to appear in Physical Review D

The leading order correction to the metric of a Schwarzschild black hole, due to the backreaction of infalling fermionic matter fields, is shown to produce a shift of the event horizon such that particles that would constitute Hawking radiation at late retarded times are now trapped. Fermionic field operators associated with infalling and outgoing modes at the horizon behave canonically in the semiclassical approximation. They are, however, shown to satisfy a nontrivial exchange algebra given in terms of the backreaction, when the shift is `quantized' by means of correspondence. The consequent exchange algebra for bilinear fermionic densities is also obtained., Comment: 16 pages, REVTEX

We give several pieces of evidence to show that extremal black holes cannot be obtained as limits of non-extremal black holes. We review arguments in the literature showing that the entropy of extremal black holes is zero, while that of near-extremal ones obey the Bekenstein-Hawking formula. However, from the counting of degeneracy of quantum (BPS) states of string theory the entropy of extremal stringy black holes obeys the area law. An attempt is made to reconcile these arguments., Comment: 18 pages, RevTEX; last section modified, version to appear in Mod. Phys. Lett. A