arXiv subjects

Jyatsnasree Bora

Publications and source records attributed to Jyatsnasree Bora.

15 recordsLinked to original sources

arXiv2026

Equatorial Periodic Orbits and Gravitational Wave Phenomenology around Spherically-symmetric vacuum solution in Freund-Nambu scalar-tensor gravity

We investigate test particle dynamics and gravitational wave (GW) phenomenology in an exact spherically symmetric vacuum solution of Freund - Nambu scalar - tensor gravity. This framework generalizes the Janis - Newman - Winicour (JNW) naked singularity via a geometric non - linear coupling $q$ and a direct scalar - particle coupling $g_s$. We demonstrate that these parameters systematically modify the Innermost Stable Circular Orbit (ISCO) - which shifts inward for $g_s > 0$ - and the Marginally Bound Orbit (MBO). Furthermore, we classify bound periodic trajectories to isolate extreme zoom - whirl orbits exhibiting intense periapsis precession. By applying the Numerical Kludge method to Extreme Mass - Ratio Inspirals (EMRIs), we reveal that scalar - tensor corrections induce a macroscopic temporal dephasing in high - frequency GW bursts, even when the orbit's spatial topology is preserved. These unique phase shifts offer a robust diagnostic signature for future space-based observatories like LISA to probe the strong - field regime and constrain scalar - tensor extensions of general relativity.

gr-qc↗

arXiv2026

Joule-Thomson effect and Efficiency of deformed AdS-Schwarzschild black hole in presence of quintessence

We study the Joule-Thomson expansion and extended thermodynamics of a modified black hole characterised by the parameters $α$, $β$, and $σ$. Analysis of the Hawking temperature, Joule-Thomson coefficient, inversion curves, and isenthalpic trajectories shows that these parameters significantly modify the heating-cooling behaviour and thermal stability of the system. The deformation parameter $α$ and control parameter $β$ shift the temperature minimum, enlarge the cooling region, and raise the inversion temperature, while $σ$ produces a weaker but consistent influence. The heat-engine analysis reveals that $α$ enhances efficiency, whereas higher $β$ and $σ$ reduce it. Overall, the results demonstrate that geometric deformation and quintessence jointly govern the unified thermodynamic structure of the black hole.

gr-qc↗

arXiv2026

Equatorial periodic orbits and gravitational wave signatures in Euler-Heisenberg black holes surrounded by perfect fluid dark matter

We investigate equatorial periodic orbits and their gravitational wave radiation in the spacetime of an Euler--Heisenberg (EH) black hole surrounded by perfect fluid dark matter (PFDM). The combined effects of quantum electrodynamic corrections and dark matter are incorporated through an effective metric, and the dynamics of timelike geodesics are analyzed using the effective potential formalism. We derive the conditions for marginally bound and innermost stable circular orbits, classify periodic trajectories using the rational parameter and topological indices, and identify a rich hierarchy of zoom--whirl motions in the strong-field regime. Gravitational wave signals from periodic orbits are computed using the numerical kludge method, revealing characteristic burst-like features associated with whirl phases. Our results show that perfect fluid dark matter systematically modifies the stability thresholds and suppresses the waveform amplitude, while QED corrections enhance high-frequency components generated near the horizon. These findings demonstrate that periodic orbits in the EH--PFDM spacetime provide a sensitive probe of quantum corrections and dark matter effects in strong gravitational fields.

gr-qc↗

arXiv2025

Thermodynamics of deformed AdS-Schwarzschild black holes in the presence of Thermal fluctuations

This paper examines the thermodynamic properties and stability of deformed AdS-Schwarzschild black holes, focusing on the effects of deformation ($α$) and thermal correction parameters ($β_1$, $β_2$) on phase transitions and heat capacity. The results show that higher $α$ values raise the Hawking-Page critical temperature, enhancing thermal stability. Thermal corrections significantly affect smaller black holes but minimally impact larger ones, leaving second-order phase transitions unchanged. Heat capacity analysis identifies stability regions, with sign changes marking instability. These findings highlight the role of deformation and thermal corrections in black hole stability, offering insights for extending our understanding of black hole thermodynamics.

hep-th↗

arXiv2025

Optical, Dynamic and Topological Characteristics of Deformed Schwarzschild Black Holes

We investigate the temperature, photon and shadow radii, quasinormal modes (QNMs), time domain profiles, greybody factors, emission rates and topological characteristics of deformed black holes, focusing on the effects of the deformation parameter $ α$ and control parameter $ β$. Increasing $ α$ enhances the oscillation frequency and damping rate of gravitational waves, while $ β$ shows non-linear behaviour. Electromagnetic perturbations exhibit similar trends, though with lower frequencies and damping rates. Greybody factors are mainly influenced by multipole moment $l$ and $ α$, with $ β$ having a more subtle effect. These findings provide insights into black hole dynamics, mergers, and gravitational wave emissions.

hep-th↗

arXiv2024

Corrected Thermodynamics and Stability of Magnetic charged AdS Black Holes surrounded by Quintessence

In this study, we explore the corrected thermodynamics of non-linear magnetic charged anti-de Sitter (AdS) black holes surrounded by quintessence, incorporating thermal fluctuations and deriving the corrected thermodynamic potentials. We analyze the effects of corrections due to thermal fluctuations on various thermodynamic potentials, including enthalpy, Helmholtz free energy, and Gibbs free energy. Our results show significant impacts on smaller black holes, with first-order corrections destabilizing them, while second-order corrections enhance stability with increasing parameter values. The specific heat analysis further elucidates the stability criteria, indicating that the large black holes ensure stability against phase transitions. However, the thermal fluctuations do not affect the physical limitation points as well as the second-order phase transition points of the black hole. Our findings highlight the intricate role of thermal fluctuations in black hole thermodynamics and their influence on stability, providing deeper insights into the behaviour of black holes under corrected thermodynamic conditions.

gr-qc↗

arXiv2024

Impact of energy-momentum conservation violation on the configuration of compact stars and their GW echoes

This work investigates the impacts of energy-momentum conservation violation on the configuration of strange stars constraint with gravitational wave (GW) event GW190814 as well as eight recent observations of compact objects. The GW echoes from these interesting classes of compact objects are also calculated. To describe the matter of strange stars, we have used two different equations of state (EoSs): first an ad-hoc exotic EoS, the stiffer MIT Bag model and next realistic CFL phase of quark matter EoS. We choose Rastall gravity as a simple model with energy-momentum conservation violation with a set of model parameter values. Our results show that this gravity theory permits stable solutions of strange stars and the resulting structures can foster GW echoes. We illustrate the implication of the gravity theory and found that the negative values of the Rastall parameter result in more compact stellar configurations and lower GW echo frequency. With an increase in the Rastall parameter, both the compactness of the stellar configurations and echo time decrease. It is worth mentioning here that with the chosen set of some probable strange star candidates from observational data and also in light of GW 190814, we have evaluated the radii of stellar models. Also, the GW echo frequencies associated with strange stars are found to be in the range of {$\approx 9-27$ kHz} for both cases. {From this work, it is also inferred that the assumption regarding the equivalence of Rastall's theory to Einstein's theory is refuted as we have noticed many deviations in the physical properties of the considered compact stars.

gr-qc↗

arXiv2023

Quasinormal Modes and Optical Properties of 4-D black holes in Einstein Power-Yang-Mills Gravity

This paper explores the impact of the Yang-Mills charge parameter and the exponent term on a $4$D black hole solution in the Einstein Power-Yang-Mills theory. Through an investigation of the massless scalar quasinormal mode spectrum, black hole shadow, and emission rate, we have determined that the effects of these two parameters are opposite. Specifically, the Yang-Mills charge parameter causes an increase in the real quasinormal frequencies with a correspondingly smaller damping rate. It also results in a smaller black hole shadow and a lower evaporation rate.

gr-qc↗

arXiv2023

Deflection angle, quasinormal modes and optical properties of a de Sitter black hole in $f(\mathcal{T}, \mathcal{B})$ gravity

The current study aims to examine the impact of the boundary term on the bending angle of light for a static spherically symmetric black hole in the modified gravity described by the $f(\mathcal{T}, \mathcal{B})$ function. To accomplish this objective, we employ the Ishihara \textit{et al.}~method, which enables us to compute the deflection angle of light for a receiver and source situated at finite distances from a lens object in a non-asymptotically flat spacetime. This method considers the receiver's viewpoint, and the resulting deflection angle diverges as the distance from the lens object increases, owing to the non-asymptotically flat spacetime. Nevertheless, the divergence can be regulated by the boundary term parameter $c_0$. For lower values of the parameter $c_0$, the divergence can be minimized within the finite range of the observer and source. Furthermore, we calculate the quasinormal modes of massless scalar perturbations in the black hole's background using the asymptotic iteration method (AIM) and Padé averaged sixth-order Wentzel-Kramers-Brillouin (WKB) approximation method. Our findings indicate that the real quasinormal modes and damping rates are significantly impacted by the model parameter $c_0$. Subsequently, we investigate two optical characteristics of the black hole, namely the shadow and the emission rate. Our results show that with an increase in the boundary term parameter $c_0$, the shadow's size increases, and the evaporation rate decreases.

gr-qc↗

arXiv2023

Joule-Thomson expansion and Optical behaviour of Reissner-Nordström-Anti-de Sitter black holes in Rastall gravity surrounded by a Quintessence field

This paper deals with the thermodynamics, Joule-Thomson expansion and optical behaviour of a Reissner-Nordström-anti-de Sitter black hole in Rastall gravity surrounded by a quintessence field. The black hole solution obtained in this framework is different from a corresponding black hole in General Relativity. The black hole metric function, as well as the Hawking temperature, is affected by the presence of energy-momentum conservation violation. The presence of energy-momentum conservation violation also affects the isenthalpic and inversion temperature curves, and with an increase in the Rastall parameter, the inversion temperature rises slowly. The impacts of other parameters, such as charge, structural constant etc., are investigated and compared. The black hole shadow, as well as the energy emission rate of the black hole, decreases with an increase in the Rastall parameter. Hence, the black holes evaporate slowly in presence of energy-momentum conservation violation.

gr-qc↗

arXiv2022

Gravitational wave echoes from strange stars for various equations of state

The tentative Gravitational Wave Echo (GWE) at a frequency of about $72\,Hz$ has been recently claimed at $4.2σ$ significance level in the GW170817 event. GWEs can be used as a tool to study the characteristics of ultra-compact stellar objects. Considering the final ultra-compact, post-merger object as a strange star, the GWE frequency can be calculated. However, GWEs are observed for only those compact stellar structures whose compactness lies in between 0.33 and 0.44. Alternatively, GWE can be obtained for those compact stars which feature a photon sphere and compactness not crossing the Buchdahl's limit radius $R_{B}=9/4M$. A photon sphere is a surface located at $R=3M$, $R$ being the radius and $M$ is the total mass of the ultra-compact object. Recently using the simplest MIT Bag model Equation of State (EoS) it has been reported that strange stars can produce GWEs with frequencies of tens of kilohertz. In view of this, for a comparative study, we have calculated the respective echo frequencies associated with strange stars by considering three models of strange star EoSs, viz., MIT bag model, linear and polytropic EoSs \cite{JB}. We found that, not being too stiff the polytropic EoS can not emit GWE, whereas the MIT Bag model and the linear EoSs can emit GWEs at a frequency range of about tens of kilohertz. Also, GWE frequency increases with the increase in values of bag constant $B$ and decreases with the increasing values of linear constant $b$. So a model-dependent nature of GWE frequencies is observed.

gr-qc↗

arXiv2022

Gravitational wave echoes from compact stars in $f(\mathcal{R},T)$ gravity

We have calculated the static and spherically symmetric solutions for compact stars in the $f(\mathcal{R},T)$ gravity metric formalism. To describe the matter of compact stars, we have used the MIT Bag model equation of state (EoS) and the color-flavor-locked (CFL) EoS. Solving the hydrostatic equilibrium equations i.e., the modified TOV equations in $f(\mathcal{R},T)$ gravity, we have obtained different stellar models. The mass-radius profiles for such stars are eventually discussed. The stability of these configurations are then analysed using different parameters. From the obtained solutions of TOV equations for mass and radius, we have checked the compactness of such objects. It is found that similar to the unrealistic EoS, like the stiffer form of the MIT Bag model, under some considerations the realistic interacting quark matter CFL EoS can give stellar structures which are compact enough to possess a photon sphere outside the stellar boundary and hence can echo GWs. The obtained echo frequencies are found to lie in the range of 39-55 kHz. Also we have shown that for different parametrizations of the gravity theory, the structure of stars and also the echo frequencies differ significantly. Moreover, we have constrained the pairing constant value $β$ from the perspective of emission of echo frequencies. For the stiffer MIT Bag model $β\geq-2.474$ and for the CFL phase with massless quark condition $β\geq-0.873$, whereas for the massive case $β\geq-0.813$.

gr-qc↗

arXiv2022

Strange stars in $f(\mathcal{R})$ gravity Palatini formalism and gravitational wave echoes from them

The compact stars are promising candidates associated with the generation of gravitational waves (GWs). In this work, we study a special type of compact stars known as strange stars in the $f(\mathcal{R})$ gravity Palatini formalism. Here we consider three promising $f(\mathcal{R})$ gravity models viz., Starobinsky, Hu-Sawicki and Gogoi-Goswami models in the domain of MIT Bag model and linear equations of state (EoSs). We compute the stellar structures numerically and constrained the $f(\mathcal{R})$ model parameters with a set of probable strange star candidates. The study shows that the consideration of stiffer MIT Bag model and linear EoSs within a favourable set of $f(\mathcal{R})$ gravity model parameters may result in strange stars with sufficient compactness to produce echoes of GWs. Thus, we have computed the GWs echo frequencies and characteristic echo times for such stars. It is found that in compliance with the experimentally obtained possible strange star candidates, the obtained GW echo frequencies for all the models are in the range of $65 - 85$ kHz.

gr-qc↗

arXiv2022

Radial oscillations and gravitational wave echoes of strange stars with nonvanishing lambda

We study the effect of the cosmological constant on radial oscillations and gravitational wave echoes (GWEs) of non-rotating strange stars. To depict strange star configurations we used two forms of equations of state (EoSs), viz., the MIT Bag model EoS and the linear EoS. By taking a range of positive and negative values of cosmological constant, the corresponding mass-radius relationships for these stars have been calculated. For this purpose, first we solved the Tolman-Oppenheimer-Volkoff (TOV) equations with a non-zero cosmological constant and then we solved the pressure and radial perturbation equations arising due to radial oscillations. The eigenfrequencies of the fundamental $f$-mode and first 22 pressure $p$-modes are calculated for each of these EoSs. Again considering the remnant of the GW170817 event as a strange star, the echo frequencies emitted by such stars in presence of the cosmological constant are computed. From these numerical calculations, we have inferred relations between cosmological constant and mode frequency, structural parameters, GWE frequencies of strange stars. Our results show that for strange stars, the effective range of cosmological constant is $10^{-15}\, \mbox{cm}^{-2} \le\,Λ\, \le 3\times 10^{-13}\, \mbox{cm}^{-2}$.

gr-qc↗

arXiv2021

Radial oscillations and gravitational wave echoes of strange stars for various equations of state

We study the radial oscillations of non-rotating strange stars and their characteristic echo frequencies for three Equations of state (EoSs), viz., MIT Bag model EoS, linear EoS and polytropic EoS. The frequencies of radial oscillations of these compact stars are computed for these EoSs. 22 lowest radial frequencies for each of these three EoSs have been computed. First, for each EoS, we have integrated Tolman-Oppenheimer-Volkoff (TOV) equations numerically to calculate the radial and pressure perturbations of strange stars. Next, the mass-radius relationships for these stars are obtained using these three EoSs. Then the radial frequencies of oscillations for these EoSs are calculated. Further, the characteristic gravitational wave echo frequencies and the repetition of echo frequencies of strange stars are computed for these EoSs. Our numerical results show that the radial frequencies and also echo frequencies vastly depend on the model and on the value of the model parameter. Our results also show that, the radial frequencies of strange stars are maximum for polytropic EoS in comparison to MIT Bag model EoS and linear EoS. Moreover, strange stars with MIT Bag model EoS and linear EoS are found to emit gravitational wave echoes. Whereas, strange stars with polytropic EoS are not emitting gravitational wave echoes.

gr-qc↗