arXiv subjects

Muktajyoti Saha

Publications and source records attributed to Muktajyoti Saha.

9 recordsLinked to original sources

arXiv2026

Logarithmic corrections to the entropy of near-extremal rotating black holes

An interesting feature of quantum corrections to the Bekenstein--Hawking entropy is the appearance of logarithmic area terms, whose coefficients are governed by the spectrum of massless fields. For near-extremal black holes, the entropy also receives a logarithmic temperature correction, whose coefficient is determined by the zero modes of the corresponding extremal black holes. In this paper, we study near-extremal rotating black holes in three, four, and five dimensions with an important focus on rotational zero modes. For three-dimensional BTZ black holes, our results are in agreement with the microscopic description. Furthermore, by treating the cosmological constant scale $\ell$ as an independent parameter, we find an additional $\log \ell$ correction to the entropy at extremality. For the five-dimensional BMPV black hole, we explicitly construct all the extremal zero modes and use them to evaluate the log temperature corrections to the entropy.

hep-th↗

arXiv2026

Logarithm of charge ratio in black hole entropy

Logarithmic correction to BPS black hole entropy, computed from microscopic description, often contains terms involving large ratios of charges, besides the logarithmic terms involving the overall scale of the charges. If the electric charges are much larger than the magnetic charges, then the attractor value of the string coupling is small and one might hope to use weakly coupled string theory to compute logarithmic corrections involving ratios of charges from the macroscopic side. We compute these for black holes in flat space-time, preserving four supercharges, in $\mathcal{N} = 2$, $\mathcal{N}=4$ and $\mathcal{N}=8$ supersymmetric string compactifications in four dimensions. We find perfect agreement with the microscopic results in $\mathcal{N}=4$ and $\mathcal{N}=8$ theories, for which the microscopic results are known. Various stringy and statistical mechanical effects become important in this analysis, including 1) use of the correct ultra-violet cut-off (string scale instead of Planck scale), 2) correct path integral measure (ultra-local measure with appropriate dilaton dependent metric), 3) use of the correct path integral variable (Kalb-Ramond 2-form instead of the dual axion) and 4) change of ensemble (from grand canonical to microcanonical). We also verify that the measure we use is consistent with what follows from the BV formalism of string field theory.

hep-th↗

arXiv2025

Quantum evolution of de Sitter black holes near extremality

We study the evolution of charged, asymptotically de Sitter black holes close to the cold extremal branch of the phase space. We consider black hole sizes that are parametrically smaller than both their inverse temperature and the cosmological horizon. Unlike flat space, charged de Sitter black holes do not evolve towards extremality, but rather towards a thermal equilibrium with the cosmological horizon. In the low-temperature regime, the near-horizon physics can be effectively captured by a one-dimensional Schwarzian theory. This is coupled to the far-horizon de Sitter quantum field theory. Incorporating the thermal nature of the cosmological horizon, we compute the quantum energy transfer through uncharged massless scalar particles. The results significantly differ from Hawking's thermal predictions. Black holes that are hotter than the cosmological horizon emit energy at a rate lower than their asymptotically flat counterparts. Whereas much colder ones absorb energy at a nearly constant rate.

hep-th↗

arXiv2024

Logarithmic corrections to entropy of 3D cosmological solutions from celestial dual

Recently a one-dimensional Schwarzian type theory was proposed as an effective dual theory of pure gravity in (2+1) dimensional asymptotically flat spacetimes \cite{Bhattacharjee:2023sfd}. This codimension-two `celestial' dual captures the Bekenstein-Hawking entropy of bulk flat cosmologies in semiclassical limit. In this paper, we extend this analysis beyond semiclassical approximation and evaluate the one-loop exact partition function of this celestial dual theory. Our analysis results in novel nontrivial logarithmic corrections to the area term of entropy, appearing from the one-loop path integral.

hep-th↗

arXiv2024

Entropy of Flat Space Cosmologies from Celestial dual

We construct a one-dimensional dual theory that effectively describes the sector of the (2+1)D flat gravity phase space near a Flat Space Cosmology (FSC) saddle labeled by definite mass and angular momentum. This Schwarzian type action describes the dynamics of the (Pseudo-) Goldstone Bosons of BMS$_3$ algebra on a circle as the symmetry is spontaneously and anomalously broken. This 1D theory, living on the celestial circle, provides an explicit construction of a celestial dual in (2+1)D. We use it to calculate the semiclassical entropy of Flat Space Cosmologies and find perfect agreement with existing literature.

hep-th↗

arXiv2024

Logarithmic corrections for near-extremal black holes

We present the computation of logarithmic corrections to near-extremal black hole entropy from one-loop Euclidean gravity path integral around the near-horizon geometry. We extract these corrections employing a suitably modified heat kernel method, where the near-extremal near-horizon geometry is treated as a perturbation around the extremal near-horizon geometry. Using this method we compute the logarithmic corrections to non-rotating solutions in four dimensional Einstein-Maxwell and $\mathcal{N} = 2,4,8$ supergravity theories. We also discuss the limit that suitably recovers the extremal black hole results.

hep-th↗

arXiv2023

Revisiting Leading Quantum Corrections to Near Extremal Black Hole Thermodynamics

Computing the 4D Euclidean path integral to one-loop order we find the large quantum corrections that govern the behavior of a spherically symmetric non-supersymmetric near-extremal black hole at very low temperature. These corrections appear from the near-horizon geometry of the near-extremal black hole. Using first-order perturbation theory we find that such corrections arise from the zero modes of the extremal background. In the logarithm of the partition function, these correspond to terms involving logarithm of temperature. Part of our result matches with the existing one in literature derived from an effective Schwarzian theory.

hep-th↗

arXiv2023

JT gravity from holographic reduction of 3D asymptotically flat spacetime

We attempt to understand the CFT$_1$ structure underlying (2+1)D gravity in flat spacetime via dimensional reduction. We observe that under superrotation, the hyperbolic (and dS$_2$) slices of flat spacetime transform to asymptotically (A)dS$_2$ slices. We consider a wedge region bounded by two such surfaces as End-of-the-World branes and employ Wedge holography to perform holographic reduction. We show that once we consider fluctuating branes, the localised theory on the branes is Jackiw-Teitelboim (JT) theory. Finally, using the dual description of JT, we derive an 1D Schwarzian theory at the spatial slice of null infinity. In this dual Celestial (nearly) CFT, the superrotation mode of 3D plays the role of the Schwarzian derivative of the boundary time reparametrization mode.

hep-th↗

arXiv2021

Equivalence of JT Gravity and Near-extremal Black Hole Dynamics in Higher Derivative Theory

Two derivative Jackiw Teitelboim gravity theory captures the near horizon dynamics of higher dimensional near extremal black holes, which is governed by a Schwarzian action at the boundary in the near horizon region. The partition function corresponding to this boundary action correctly gives the statistical entropy of the near extremal black hole. In this paper, we study the thermodynamics of spherically symmetric four dimensional near extremal black holes in presence of arbitrary perturbative four derivative corrections. We find that the near horizon dynamics is again captured by a JT like action with a particular namely square of Ricci scalar higher derivative modification. Effectively the theory is described by a boundary Schwarzian action which gets suitably modified due to the presence of the higher derivative interactions. Near extremal entropy, free energy also get corrected accordingly.

hep-th↗