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Sauvik Sen

Publications and source records attributed to Sauvik Sen.

14 recordsLinked to original sources
arXiv2026

Entropy bounds, Geroch process, and the sign of deformation parameter

Based on Geroch's process of dropping a system into a black hole from the vicinity of the horizon, we investigate in this paper the influence of deformation on the Bekenstein entropy bound both for (3+1) and (2+1) dimensions in the context of a generalized uncertainty principle (GUP). While providing a coherent framework that sets an upper limit on the entropy across dimensions we show, within a semiclassical treatment, that while a negative GUP deformation yields a universal relaxation of the bound, a positive deformation tightens it. Our results may be interpreted as a response to Planck-scale modifications of the near-horizon redshift.

hep-th↗
arXiv2026

Dimming of Photon Ring due to Photon-Axion Conversion around Kerr Black Holes

We investigate photon-axion conversion in the vicinity of rotating Kerr black holes where strong gravity traps photons on near-circular trajectories, effectively enhancing the path length. We explore the observable signatures of such a conversion near the photon region. The process, driven by ambient magnetic fields, is significantly more efficient around supermassive black holes such as M87*, since the luminosity of photons increases with the mass of the BH. By numerically evaluating photon path lengths (on which the conversion depends), we analyze how key parameters-photon frequency, axion mass, photon-axion coupling, magnetic field strength, plasma density, and black hole spin-affect the conversion probability and the resultant dimming of photon spectral luminosity. We find that the conversion is most efficient at high frequencies (X-rays and gamma rays), while the frequency window associated with efficient conversion widens with an increase in the photon-axion coupling and a decrease in the electron density and the axion mass. The magnitude of dimming of the photon spectral luminosity depends primarily on the magnetic field, the photon-axion coupling and the BH spin. Our study reveals that rotating black holes generally exhibit enhanced dimming compared to static ones. Thus, if future telescopes achieving a resolution $\sim 10^{-5}$ arcsec in the X-ray/gamma-ray band detect a dimming of the photon spectral luminosity, then they can provide interesting constraints on the axion mass and its coupling with photons.

gr-qc↗
arXiv2025

Painlev\'{e}-Gullstrand coordinates for Kiselev black holes

We investigate the implications provided by the modified Painlev\'{e}-Gullstrand coordinates in the context of quintessence for the Kiselev black hole. In this regard, we set up a fully static line element in terms of lapse and shift functions, apart from including the deformation parameter signaling deviation from the standard Painlev\'{e}-Gullstrand metric. We address two specific issues pertaining to the problems of radiation and dust furnished by the corresponding barotropic index parameter and study the related consequences by performing a range of analyses to explore the influence imposed by quintessence. We also discuss the thermodynamical consequences by evaluating the expressions of the Hawking temperature and the entropy function in closed forms.

gr-qc↗
arXiv2024

Quantum tunneling driven by quintessence and the role of GUP

In this paper, we studied quantum tunneling of massless and massive particles pertaining to a Schwarzschild black hole in a quintessence background, and explored the consequences emerging from a generalized uncertainty principle (GUP). For the quintessence scenario, we considered two specific cases of $w$, which is the ratio of the pressure and energy density, namely $w=-1/3$ and $w=-2/3$. For the GUP, we used a modified Schwarzschild metric and employed a unique choice of contour integration to compute the tunneling amplitudes. An analysis and comparative study of the respective temperature profiles has been made. The energy emission rate has also been analysed.

gr-qc↗
arXiv2024

Landauer's principle and black hole area quantization

This article assesses Landauer's principle from information theory in the context of area quantization of the Schwarzschild black hole. Within a quantum-mechanical perspective where Hawking evaporation can be interpreted in terms of transitions between the discrete states of the area (or mass) spectrum, we justify that Landauer's principle holds consistently in the saturated form when the number of microstates of the black hole goes as $2^n$, where $n$ is a large positive integer labeling the levels of the area/mass spectrum in the semiclassical regime. This is equivalent to the area spacing $\Delta A = \alpha l_P^2$ (in natural units), where $\alpha = 4 \ln 2$ for which the entropy spacing between consecutive levels in Boltzmann units coincides exactly with one bit of information. We also comment on the situation for other values of $\alpha$ prevalent in the literature.

gr-qc↗
arXiv2024

Quantized Area of the Schwarzschild Black Hole: A non-Hermitian Perspective

In this work, our aim is to link Bekenstein's quantized form of the area of the event horizon to the Hamiltonian of the non-Hermitian Swanson oscillator which is known to be $\mathbb{PT}$-symmetric. We achieve this by employing a similarity transformation that maps the non-Hermitian quantum system to a scaled harmonic oscillator. Our procedure is standard and well known. We, first of all, consider the unconstrained reduced Hamiltonian which is directly expressed in terms of the Schwarzschild mass and implies a periodic character for the conjugate momentum (which represents the asymptotic time coordinate), the period being the inverse Hawking temperature. This leads to the quantization of the event-horizon area in terms of the harmonic-oscillator levels. Within the framework of the Swanson oscillator, we proceed to derive novel expressions for the Hawking temperature and the black hole entropy. Notably, the logarithmic area-correction term -(1/2)$\ln$(area) is consistent with our results whereas -(3/2) $\ln$(area) is not.

gr-qc↗
arXiv2023

Analogue Hawking radiation as a tunneling in a two-level $\mathcal{PT}$-symmetric system

In the light of a general scenario of a two-level non-Hermitian $\mathcal{PT}$-symmetric Hamiltonian we apply the tetrad-based method to analyze the possibility of analogue Hawking radiation. It is done by making use of the conventional null-geodesic approach wherein the associated Hawking radiation is described as a quantum tunneling process across a classically forbidden barrier which the event horizon imposes. An interesting aspect of our result is that our estimate for the tunneling probability is independent of the non-Hermitian parameter that defines the guiding Hamiltonian.

gr-qc↗
arXiv2022

Refractive index profiles for a $\mathcal{PT}$-symmetric optical structure

By mapping the scalar Helmholtz equation (SHE) to the Sch\"{r}odinger form we investigate the behaviour of $\mathcal{PT}$ optical structure when the refractive index distribution $n$ admits variation in the longitudinal direction only. Interpreting the Sch\"{r}odinger equation in terms of a superpotential we determine the supersymmetric partners for $n$. We also obtain new analytical solutions for the refractive index profiles and provide graphical illustrations for them.

quant-ph↗
arXiv2022

MOND and asymptotic safe gravity

The modified Newtonian dynamics (MOND) paradigm is discussed in the context of asymptotic safe gravity. We estimate quantum correction to the logarithmic potential which is well known to account for the constancy of the circular velocity $v$ of the spiral galaxies. We determine plausible bounds on $v$.

gr-qc↗
arXiv2021

Tunneling of Hawking radiation for BTZ black hole revisited

We re-examine Hawking radiation for a nonrotating (2+1)-dimensional BTZ black hole and evaluate the transmission probability of tunneling through the barrier of the event horizon employing the standard method of WKB approximation. Our results are presented for both uncharged and charged cases. We also explore the associated thermodynamics in terms of Hawking temperature and provide estimates of black hole parameters like the surface gravity and entropy.

gr-qc↗
arXiv2021

Exceptional point in a coupled Swanson system

We propose an interacting nonhermitian model described by a two-mode quadratic Hamiltonian along with an interaction term to locate and analyze the presence of an exceptional point in the system. Each mode is guided by a Swanson-like quadratic Hamiltonian and a suitable choice is made for the interaction term. The parity-time symmetric transformation is adopted in the standard way relevant for a coupled system.

quant-ph↗
arXiv2021

Hawking radiation for a (2+1)-dimensional spinning black hole and the issue of tunneling

We examine Hawking radiation for a (2+1)-dimensional spinning black hole and study the interesting possibility of tunneling through the event horizon which acts as a classically forbidden barrier. Our finding shows it to be much lower than its nonrotating counterpart. We further explore the associated thermodynamics in terms of Hawking temperature and give estimates of black hole parameters like the surface gravity and entropy.

gr-qc↗