arXiv subjects

Krishna Jalan

Publications and source records attributed to Krishna Jalan.

4 recordsLinked to original sources

arXiv2026

Wald-like entropy and Islands in Dimensionally Reduced Einstein-Hilbert Gravity

We study the island formula and Page curve for the asymptotically flat eternal and quasi-stationary evaporating black hole solutions within the dimensionally reduced Einstein-Hilbert (DREH) model. In this model, the four-dimensional Einstein-Hilbert action reduces to a two-dimensional dilaton gravity, on top of which the quantum corrections can be incorporated via the Polyakov-Liouville (PL) action for a two-dimensional conformal field theory with a large central charge $c$. This gravity model arises from the s-wave approximation of four-dimensional Einstein-Hilbert gravity and provides a fully gravitational setting in which we study the islands, i.e., we will not require a non-gravitational bath region to collect the radiation, instead it lives in the black hole spacetime itself. The fine-grained entropy of Hawking radiation in the eternal and evaporating black holes within the DREH model was derived using the island rule in \cite{djordjevic2022eternal, djordevic2025evaporating}. The island rule is based on the replica method using the Euclidean gravitational path integral. In this work, we complement the Euclidean approach by providing a Lorentzian prescription for the generalized entropy $S_{\text{gen}}$, in the island formula without invoking the replica trick to compute $S_{\text{gen}}$. The generalized entropy is shown to coincide with Wald-like Noether charge of the combined DREH-PL action. Using this generalized entropy, we determine the quantum extremal surface, the Page time, and the Page curve for the eternal and the evaporating black hole. We conclude with a discussion of the possible extension to the full four-dimensional geometry incorporating vacuum polarization corrections.

hep-th↗

arXiv2024

Island Paradigm and Information Recovery from Radiation

The island paradigm for an AdS$_2$ eternal black hole in the Hartle-Hawking state coupled to a finite temperature non-gravitating bath asserts that after the Page time the operators in the black hole interior can be reconstructed using the bath degrees of freedom. We demonstrate this assertion by consideing a special operator $\mathbb{U}_{bath}$ that has nontrivial action only on the bath degrees of freedom. We show via the gravitational Euclidean path integral analysis that though before the Page time $\mathbb{U}_{bath}$ does not translate the operators in the bath to the black hole interior, after the Page time it takes them to the black hole interior.

hep-th↗

arXiv2023

Reduced Half-sided Translations and Islands

An AdS$_2$ black hole in equilibrium with a finite temperature non-gravitating bath comes with a Hawking-like information paradox. The resolution of this paradox requires introducing an island for the bath after the Page time. Since the island region contains the black hole interior, the consistency of the island paradigm demands the failure of any interior reconstruction proposal that uses only the operators in the AdS$_2$ region outside the black hole horizon after the Page time. In this paper, we investigate the consistency of the island paradigm using the black hole interior reconstruction proposal due to Leutheusser and Liu. They argued that the operators in the interior of a black hole can be reconstructed by the half-sided translations of the operators outside the black hole horizon. However, in order to illustrate the island paradigm we need to modify the Leutheusser-Liu proposal by introducing the notion of the reduced half-sided translations. The reduced half-sided translations, unlike the half-sided translations, have non-trivial action only on the operators in the AdS$_2$ black hole region. As a result, the reconstructed interior operators are expressed only using the operators in the AdS$_2$ region outside the black hole horizon. We demonstrate the consistency of the island paradigm by showing that the reduced half-sided translation, which successfully reconstruct the operators in the black hole interior before the Page time, fails to reconstruct the interior operators after the Page time.

hep-th↗

arXiv2023

Generalized Second Law for Non-minimally Coupled Matter Theories

We prove the generalized second law (GSL) for higher curvature gravity theories when the matter sector is non-minimally coupled. The validity of our proof is in the regime of linearized fluctuations about equilibrium black holes, which is the same regime as considered in the previous proofs by Wall and Sarkar. These proofs were provided in different gravity theories - for instance, Lovelock theory and higher curvature gravity - but the matter sector was always taken to be minimally coupled. In this article, we describe how to generalize the proof of linearized semi-classical GSL when the matter sector comes with non-minimal couplings. The proof proceeds by suitably evaluating the matter path integral in the stress tensor expectation value by treating the higher derivative couplings in an effective field theory setting. We use the recently established result of the linearized second law for such theories.

gr-qc↗