arXiv subjects

Saurya Das

Publications and source records attributed to Saurya Das.

At least 127 records · Page 7Linked to original sources

arXiv2008

Power-law corrections to entanglement entropy of horizons

We re-examine the idea that the origin of black-hole entropy may lie in the entanglement of quantum fields between inside and outside of the horizon. Motivated by the observation that certain modes of gravitational fluctuations in a black-hole background behave as scalar fields, we compute the entanglement entropy of such a field, by tracing over its degrees of freedom inside a sphere. We show that while this entropy is proportional to the area of the sphere when the field is in its ground state, a correction term proportional to a fractional power of area results when the field is in a superposition of ground and excited states. The area law is thus recovered for large areas. Further, we identify location of the degrees of freedom that give rise to the above entropy.

gr-qc↗

arXiv2008

Gravitational non-commutativity and Gödel-like spacetimes

We derive general conditions under which geodesics of stationary spacetimes resemble trajectories of charged particles in an electromagnetic field. For large curvatures (analogous to strong magnetic fields), the quantum mechanicical states of these particles are confined to gravitational analogs of {\it lowest Landau levels}. Furthermore, there is an effective non-commutativity between their spatial coordinates. We point out that the Som-Raychaudhuri and Gödel spacetime and its generalisations are precisely of the above type and compute the effective non-commutativities that they induce. We show that the non-commutativity for Gödel spacetime is identical to that on the fuzzy sphere. Finally, we show how the star product naturally emerges in Som-Raychaudhuri spacetimes.

hep-th↗

arXiv2007

Power-law corrections to black-hole entropy via entanglement

We consider the entanglement between quantum field degrees of freedom inside and outside the horizon as a plausible source of black-hole entropy. We examine possible deviations of black hole entropy from area proportionality. We show that while the area law holds when the field is in its ground state, a correction term proportional to a fractional power of area results when the field is in a superposition of ground and excited states. We compare our results with the other approaches in the literature.

gr-qc↗

arXiv2007

Where are the black hole entropy degrees of freedom ?

Understanding the area-proportionality of black hole entropy (the `Area Law') from an underlying fundamental theory has been one of the goals of all models of quantum gravity. A key question that one asks is: where are the degrees of freedom giving rise to black hole entropy located? Taking the point of view that entanglement between field degrees of freedom inside and outside the horizon can be a source of this entropy, we show that when the field is in its ground state, the degrees of freedom near the horizon contribute most to the entropy, and the area law is obeyed. However, when it is in an excited state, degrees of freedom far from the horizon contribute more significantly, and deviations from the area law are observed. In other words, we demonstrate that horizon degrees of freedom are responsible for the area law.

gr-qc↗

arXiv2007

Where are the degrees of freedom responsible for black hole entropy?

Considering the entanglement between quantum field degrees of freedom inside and outside the horizon as a plausible source of black hole entropy, we address the question: {\it where are the degrees of freedom that give rise to this entropy located?} When the field is in ground state, the black hole area law is obeyed and the degrees of freedom near the horizon contribute most to the entropy. However, for excited state, or a superposition of ground state and excited state, power-law corrections to the area law are obtained, and more significant contributions from the degrees of freedom far from the horizon are shown.

gr-qc↗

arXiv2007

Entanglement as a source of black hole entropy

We review aspects of black hole thermodynamics, and show how entanglement of a quantum field between the inside and outside of a horizon can account for the area-proportionality of black hole entropy, provided the field is in its ground state. We show that the result continues to hold for Coherent States and Squeezed States, while for Excited States, the entropy scales as a power of area less than unity. We also identify location of the degrees of freedom which give rise to the above entropy.

gr-qc↗

arXiv2006

Randall-Sundrum with Kalb-Ramond field: return of the hierarchy problem?

We show that when the antisymmetric Kalb-Ramond field is included in the Randall-Sundrum scenario, although the hierarchy problem can be solved, it requires an extreme fine tuning of the Kalb-Ramond field (about 1 part in $10^{62}$). We interpret this as the return of the problem in disguise. Further, we show that the Kalb-Ramond field induces a small negative cosmological constant on the visible brane.

gr-qc↗

arXiv2006

Gravitational Anomalies, Hawking Radiation, and Spherically Symmetric Black Holes

Motivated by the recent work of Robinson and Wilczek, we evaluate the gravitational anomaly of a chiral scalar field in a Vaidya spacetime of arbitrary mass function, and thus the outgoing flux from the time-dependent horizon in that spacetime. We show that this flux differs from that of a perfect blackbody at a fixed temperature. When this flux is taken into account, general covariance in that spacetime is restored. We also generalize their results to the most general static, and spherically symmetric spacetime.

hep-th↗

arXiv2006

Readdressing the hierarchy problem in a Randall-Sundrum scenario with bulk Kalb-Ramond background

We re-examine the fine tuning problem of the Higgs mass, when an antisymmetric two form Kalb-Ramond (KR) field is present in the bulk of a Randall-Sundrum (RS) braneworld. Taking into account the back-reaction of the KR field, we obtain the exact correction to the RS metric. The modified metric also warps the Higgs mass from Planck scale (in higher dimension) to TeV scale (on the visible brane) for a range of values of $kr$ exceeding the original RS value (where $k=$ Planck mass and $r=$ size of extra dimension). However, it requires an extraordinary suppression of the KR field density, indicating the re-appearence of the fine tuning problem in a different guise. The new spacetime also generates a small negative cosmological constant on the visible brane. These results are particularly relevant for certain string based models, where the KR field is unavoidably present in the bulk. We further show that such a bulk antisymmetric KR field fails to stabilize the braneworld.

hep-th↗

arXiv2006

How robust is the entanglement entropy-area relation?

We revisit the problem of finding the entanglement entropy of a scalar field on a lattice by tracing over its degrees of freedom inside a sphere. It is known that this entropy satisfies the area law -- entropy proportional to the area of the sphere -- when the field is assumed to be in its ground state. We show that the area law continues to hold when the scalar field degrees of freedom are in generic coherent states and a class of squeezed states. However, when excited states are considered, the entropy scales as a lower power of the area. This suggests that for large horizons, the ground state entropy dominates, whereas entropy due to excited states gives power law corrections. We discuss possible implications of this result to black hole entropy.

gr-qc↗

arXiv2006

Is entanglement entropy proportional to area?

It is known that the entanglement entropy of a scalar field, found by tracing over its degrees of freedom inside a sphere of radius ${\cal R}$, is proportional to the area of the sphere (and not its volume). This suggests that the origin of black hole entropy, also proportional to its horizon area, may lie in the entanglement between the degrees of freedom inside and outside the horizon. We examine this proposal carefully by including excited states, to check probable deviations from the area law.

hep-th↗

arXiv2006

High frequency quasi-normal modes for black holes with generic singularities II: Asymptotically non-flat spacetimes

The possibility that the asymptotic quasi-normal mode (QNM) frequencies can be used to obtain the Bekenstein-Hawking entropy for the Schwarzschild black hole -- commonly referred to as Hod's conjecture -- has received considerable attention. To test this conjecture, using monodromy technique, attempts have been made to analytically compute the asymptotic frequencies for a large class of black hole spacetimes. In an earlier work, two of the current authors computed the high frequency QNMs for scalar perturbations of $(D+2)$ dimensional spherically symmetric, asymptotically flat, single horizon spacetimes with generic power-law singularities. In this work, we extend these results to asymptotically non-flat spacetimes. Unlike the earlier analyses, we treat asymptotically flat and de Sitter spacetimes in a unified manner, while the asymptotic anti-de Sitter spacetimes is considered separately. We obtain master equations for the asymptotic QNM frequency for all the three cases. We show that for all the three cases, the real part of the asymptotic QNM frequency -- in general -- is not proportional to ln(3) thus indicating that the Hod's conjecture may be restrictive.

hep-th↗

arXiv2005

Charged black holes in generalized dilaton-axion gravity

We study generic Einstein-Maxwell-Kalb-Ramond-dilaton actions, and derive conditions under which they give rise to static, spherically symmetric black hole solutions. We obtain new asymptotically flat and non-flat black hole solutions which are in general electrically and magnetically charged. They have positive definite and finite quasi-local masses. Existing non-rotating black hole solutions (including those appearing in low energy string theory) are recovered in special limits.

hep-th↗

arXiv2005

High frequency quasi-normal modes for black-holes with generic singularities

We compute the high frequency quasi-normal modes (QNM) for scalar perturbations of spherically symmetric single horizon black-holes in $(D+2)$-space-time dimensions with generic curvature singularities and having metrics of the form $ds^2 = ηx^p (dy^2-dx^2) + x^q dØ_D^2$ near the singularity $x=0$. The real part of the QN frequencies is shown to be proportional to $\log \le[ 1 + 2\cos \le(\p \le[ qD -2 \ri]/2 \ri) \ri]$ where the constant of proportionality is equal to the Hawking temperature for non-degenerate black-holes and inverse of horizon radius for degenerate black-holes. Apart from agreeing with the QN frequencies that have been computed earlier, our results imply that the horizon area spectrum for the general spherically symmetric black-holes is equispaced. Applying our results, we also find the QNM frequencies for extremal Reissner-Nordström and various stringy black-holes.

hep-th↗

arXiv2005

Spectrum of rotating black holes and its implications for Hawking radiation

The reduced phase space formalism for quantising black holes has recently been extended to find the area and angular momentum spectra of four dimensional Kerr black holes. We extend this further to rotating black holes in all spacetime dimensions and show that although as in four dimensions the spectrum is discrete, it is not equispaced in general. As a result, Hawking radiation spectra from these black holes are continuous, as opposed to the discrete spectrum predicted for four dimensional black holes.

hep-th↗

arXiv2004

How classical are TeV-scale black holes?

We show that the Hawking temperature and the entropy of black holes are subject to corrections from two sources: the generalized uncertainty principle and thermal fluctuations. Both effects increase the temperature and decrease the entropy, resulting in faster decay and ``less classical'' black holes. We discuss the implications of these results for TeV-scale black holes that are expected to be produced at future colliders.

hep-th↗

arXiv2004

Black Hole Thermodynamics: Entropy, Information and Beyond

We review some recent advances in black hole thermodynamics, including statistical mechanical origins of black hole entropy and its leading order corrections, from the viewpoints of various quantum gravity theories. We then examine the information loss problem and some possible approaches to its resolution. Finally, we study some proposed experiments which may be able to provide experimental signatures of black holes.

hep-th↗

arXiv2004

Anti-de Sitter black holes, perfect fluids, and holography

We consider asymptotically anti-de Sitter black holes in $d$-spacetime dimensions in the thermodynamically stable regime. We show that the Bekenstein-Hawking entropy and its leading order corrections due to thermal fluctuations can be reproduced by a weakly interacting fluid of bosons and fermions (`dual gas') in $Δ=α(d-2)+1$ spacetime dimensions, where the energy-momentum dispersion relation for the constituents of the fluid is assumed to be $ε= κp^α$. We examine implications of this result for entropy bounds and the holographic hypothesis.

hep-th↗