arXiv subjects

Dhruba Jyoti Gogoi

Publications and source records attributed to Dhruba Jyoti Gogoi.

At least 19 recordsLinked to original sources

arXiv2026

Dynamical Stability and Quasinormal Modes of Casimir Wormholes in dRGT Massive Gravity

This paper investigates static, spherically symmetric traversable wormholes supported by Casimir energy within de Rham-Gabadadze-Tolley (dRGT) massive gravity. By deriving the exact shape function $b(r) = r_0 + \frac{π^3(-r + r_0)}{90 r r_0} - \frac{1}{2} C m_g^2 (r - r_0)[2C c_2 + c_1(r + r_0)]$, we verify that the geometry satisfies the local Morris--Thorne throat and traversability conditions, including $b(r_0)=r_0$ and $b'(r_0)<1$. For the nonzero massive-gravity parameters considered here, the resulting spacetime is not asymptotically flat, and its large-$r$ behavior is governed by the massive-gravity contributions to the shape function. The Casimir energy density $ρ= -π^2/(720 r^4)$ ensures the Null Energy Condition is violated throughout the throat region, as demonstrated by the negative behavior of $(ρ+ p_r)$ and $(ρ- |p_r|)$ across all parameter values. Analysis of the volume integral quantifier reveals that the massive gravity parameter $m_g^2 c_2$ directly regulates the exotic matter requirement, with the integrated NEC violation becoming more negative as $m_g^2 c_2$ increases from $0.1$ to $0.5$. The mechanical equilibrium is rigorously established via the generalized Tolman-Oppenheimer-Volkoff equation, where the anisotropic force precisely balances the gravitational and hydrostatic forces. The quasinormal mode spectrum for scalar perturbations is extracted using both the analytical Mashhoon method and direct numerical integration. The effective potential forms a symmetric barrier at the throat, with the peak height increasing with the multipole number $\ell$. The damping rate $|ω_I|$ grows systematically with increasing massive gravity parameter. These distinct spectral signatures provide robust theoretical markers for distinguishing Casimir wormholes from black holes in future gravitational wave observations.

gr-qc↗

arXiv2026

Quantum-Corrected Thermodynamics and Phase Structure of AdS Euler-Heisenberg Black Hole

We investigate the thermodynamic behaviour of an AdS black hole arising from nonlinear electrodynamics-corrected gravity, incorporating quantum effects through thermal fluctuations. From the Einstein--Euler--Heisenberg framework, we consider the modified black hole solution and analyse its thermodynamic properties in the extended phase space. Logarithmic and inverse-area corrections to the entropy are obtained, leading to modified expressions for enthalpy, internal energy, Helmholtz free energy and Gibbs free energy. The corrected specific heat exhibits multiple divergences and sign changes, signalling genuine second-order phase transitions and revealing a quantum-stabilized microscopic phase followed by universal macroscopic instability. Our results demonstrate that thermal fluctuations qualitatively restructure the thermodynamic phase space and highlight the dominant role of quantum corrections in governing the black hole stability.

gr-qc↗

arXiv2026

Constraints on the Modified Emergent Dark Energy Model Using DESI DR2 BAO

In this work, we investigate the modified emergent dark energy (MEDE) model using baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument Data Release 2 (DESI DR2), together with CMB information from the {\tt LoLLiPoP} (low-$\ell$) and {\tt HiLLiPoP} (high-$\ell$) likelihoods based on the latest Planck NPIPE PR4 release, Planck PR4 lensing, ACT DR6 lensing, and three Type Ia supernova samples (Pantheon$+$, DES-Dovekie, and Union3). We find that the MEDE model remains largely consistent with the standard $Λ$CDM cosmology. Although small departures from $Λ$CDM are allowed, the inclusion of SNe~Ia data drives the model parameters toward the standard cosmological scenario, with the parameter $α$ remaining consistent with $α=0$ at the $1σ$ level. The model does not significantly alleviate the $H_0$ or $S_8$ tensions: the inferred $H_0$ values remain below the SH0ES measurement, the sound horizon $r_d$ is nearly unchanged, and the predicted $S_8$ values remain close to those of $Λ$CDM. The reconstructed cosmological evolution closely follows the $Λ$CDM prediction, with deviations generally below the $0.5σ$ level. While the CMB + DESI DR2 dataset favors a full phantom regime, the inclusion of SNe~Ia shifts the evolution toward a full quintessence regime. Finally, although the $Δχ^2_{\rm MAP}$ and $Δ{\rm AIC}$ criteria indicate a marginally better fit than $Λ$CDM, the logarithmic Bayes factor provides only inconclusive evidence in favor of the MEDE model. Overall, the MEDE model remains compatible with current observations but does not exhibit the phantom-crossing behavior suggested by recent DESI DR2 analyses.

physics.gen-ph↗

arXiv2026

Geodesic structure, eikonal quasinormal modes and thermodynamic properties of a Schwarzschild-de Sitter-like black hole with global monopole in Bumblebee gravity

We investigate the geodesic dynamics, eikonal quasinormal modes (QNMs), and extended phase space thermodynamics of a Schwarzschild-de Sitter-like black hole coupled with a global monopole in Bumblebee gravity. Our analysis reveals that spontaneous Lorentz symmetry breaking and topological defects modify the effective radial dynamics, leading to lower effective potential barriers and a reduced magnitude of the effective force. For null geodesics, higher monopole parameters expand the photon sphere and critical impact parameter, implying an enlarged black hole shadow, while mitigating dynamical instability. For massive particles, the stable circular orbit window narrows significantly as the Outermost Stable Circular Orbit (OSCO) shrinks, alongside a marked enhancement in perihelion precession. In addition, we examine the correspondence between the eikonal QNMs and the properties of null geodesics. The excellent agreement between the eikonal approximation and the WKB method for scalar and electromagnetic perturbations supports the validity of the correspondence for the spacetime under consideration. In the extended thermodynamic phase space, we evaluate the black hole as a holographic heat engine. We demonstrate that classical efficiency is mathematically blind to Lorentz violation; however, introducing a quantum-corrected modified entropy tightly couples the macroscopic work output to the symmetry-breaking framework. Ultimately, the necessity to respect the Carnot bound imposes a strict macroscopic constraint on the Lorentz-violating parameter, safeguarding the Second Law of Thermodynamics.

gr-qc↗

arXiv2026

Conformal Killing Gravity: New Constraints from DESI DR2 BAO datasets

We investigate a geometric approach referred to as the Conformal Killing Gravity (CKG), in which the dark energy sector emerges naturally from the conformal Killing symmetry of the Robertson--Walker space-time. Within this framework, the divergence-free conformal Killing tensor behaves as an effective perfect fluid, giving rise to a dynamical dark-energy component whose density, pressure, and equation of state are uniquely determined by the underlying geometry, without introducing any empirical dark-energy parametrization. The resulting CKG model extends the standard $Λ$CDM cosmology through a single additional parameter while recovering the $Λ$CDM limit in the absence of the geometric contribution. We constrain the model using Planck PR4 (NPIPE) CMB temperature, polarization, and lensing observations, ACT DR6 CMB lensing, DESI DR2 baryon acoustic oscillation measurements, and the Pantheon$+$, DES-Dovekie, and Union3 Type Ia supernova compilations. The analysis shows that the CKG favors a quintessence-like dark-energy evolution with no evidence for phantom crossing, while the reconstructed equation of state rapidly approaches the cosmological constant at earlier cosmic times. Furthermore, the model predicts a future critical redshift in the range $-0.8 \lesssim z_c \lesssim -0.7$, indicating that the present cosmic expansion eventually reaches a turning point before the formal singular limit at $z=-1$. Since the geometric contribution modifies only the post-recombination expansion history, the sound horizon remains essentially unchanged and the model does not provide a complete solution to the $H_0$ tension. Our results demonstrate that the CKG provides a simple, physically motivated, and observationally favored framework for describing the late-time accelerated expansion of the Universe.

astro-ph.CO↗

arXiv2026

No preference for generalized emergent dark energy from current cosmological data

In this work, we revisit the generalized emergent dark energy model by confronting it with DESI DR2 baryon acoustic oscillation measurements, in combination with joint CMB data from ACT, SPT, and Planck, as well as Type Ia supernova samples including Pantheon$^+$, DES-Dovekie, and Union3. We find that the GEDE model remains compatible with the $Λ$CDM paradigm, with no statistically significant preference for deviations when all datasets are combined. In particular, the key model parameter $Δ$ is consistent with the $Λ$CDM value $Δ= 0$ within $2σ$ once SNe Ia data are included. Despite this overall agreement, the GEDE model does not exhibit the phantom crossing suggested by DESI DR2. Instead, the evolution of the dark energy equation of state $w(z)$ indicates that the model behaves either as a full phantom ($w < -1$) or quintessence ($w > -1$), depending on the dataset combination, without a clear transition across $w = -1$. When Pantheon$^+$ data are included, the model converges closely to $Λ$CDM with $w \simeq -1$. The GEDE model does not alleviate the existing cosmological tensions. The inferred values of $H_0$ remain in the range $67.9$-$69.8\ \mathrm{km,s^{-1},Mpc^{-1}}$, while the sound horizon $r_d$ and clustering parameter $S_8$ remain consistent with $Λ$CDM, failing to resolve the $H_0$ and $S_8$ tensions. Finally, both Gaussian significance levels ($<2σ$) and Bayesian evidence ($\ln B_{i,j} < 1$) indicate no statistically significant preference for GEDE over $Λ$CDM. We conclude that, although DESI DR2 hints at dynamical dark energy, the GEDE model remains observationally indistinguishable from $Λ$CDM and does not support the Quintom-B-type behavior suggested by DESI DR2.

astro-ph.CO↗

arXiv2026

Testing the Anton-Schmidt dark energy model with the DESI DR2 measurements

We present a comparative cosmological analysis of the Anton-Schmidt, $Λ$CDM, and CPL models using baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument Data Release 2, combined with the Planck PR4 (NPIPE) CamSpec Cosmic Microwave Background likelihoods and three Type Ia supernova catalogues: Pantheon$+$, DES-Dovekie, and Union3. We use Markov Chain Monte Carlo analyses to constrain the parameters of the Anton-Schmidt model against each dataset combination. We find that the Anton-Schmidt model provides a good fit to current cosmological observations. The Anton-Schmidt model provides a good fit to the current cosmological observations but does not provide a significant alleviation of either the $H_0$ or the $S_8$ tensions. The Anton-Schmidt parameter is tightly constrained to $B \simeq -0.38$, indicating that the logarithmic correction becomes relevant only at late times. The Anton-Schmidt and CPL models predict quintessence-like present-day dark-energy equations of state and shows Quintom-B evolution, with their dark-energy equation-of-state parameters crossing the phantom divide at approximately $z \approx 0.5$. The characteristic density scale is constrained to be $ρ_\ast/ρ_{c,0}\sim4\text{--}5$, substantially smaller than the large density scales typically assumed in logotropic-inspired scenarios, indicating that the Anton-Schmidt correction mainly affects the late-time expansion history. Finally, Bayesian evidence shows moderate-to-strong preference for the Anton-Schmidt model over the $Λ$CDM model and strong-to-decisive preference over the CPL parametrization. Although the Anton-Schmidt model does not alleviate the current cosmological tensions, it emerges as a statistically favored dynamical dark-energy scenario whose cosmological implications deserve further tested with forthcoming Stage-IV large-scale structure observations.

physics.gen-ph↗

arXiv2026

Multi-Spin Perturbations, Thermodynamics, and Observational Signatures of Reissner-Nordstrom Black Holes in Bumblebee Gravity

In this paper, we present a comprehensive investigation into the dynamical and thermodynamic properties of the charged Reissner-Nordström (RN) black hole (BH) in the bumblebee gravity framework, where spontaneous Lorentz symmetry breaking (LSB) occurs. To analyze the dynamical behavior, we apply the unified Teukolsky master equation within the Newman-Penrose formalism to evaluate massless field perturbations of arbitrary spins ($s=0, 1/2, 1, 3/2, 2$). By deriving the corresponding effective potentials, we compute the quasinormal modes (QNMs) frequencies using the Padé-improved 6th-order WKB approximation and the Asymptotic Iteration Method (AIM) and evaluate the greybody factors for all perturbing fields, demonstrating how the LSB parameter $L$ and the BH charge $Q$ modify the spacetime's damped oscillations and wave propagation. We further assess the observational prospects of these QNMs by determining the black-hole mass ranges accessible to current and future gravitational-wave detectors, including LISA, Virgo, and LIGO. Moreover, we investigate the modified thermodynamic structure, calculating the Hawking temperature, entropy with logarithmic thermal corrections and heat capacity. Our thermodynamic analysis reveals a second-order phase transition whose critical radius is heavily governed by the background charge. These combined findings provide valuable theoretical insights into how Lorentz violation affects the physical stability, thermal evolution, and phase structure of charged BHs.

gr-qc↗

arXiv2026

Dynamics, Ringdown, and Accretion-Driven Multiple Quasi-Periodic Oscillations of Kerr-Bertotti-Robinson Black Holes

We study the motion of test particles around the Kerr--Bertotti--Robinson (KBR) black hole (BH) and explore how the three defining parameters, the mass $M$, rotation parameter $a$, and magnetic parameter $B$ influence their dynamics. We derive analytical expressions for the energy and angular momentum of stable equatorial circular orbits, along with the corresponding radial and latitudinal oscillation frequencies, as functions of $M$, $a$, and $B$. We also examine the key features of the quasi-periodic oscillations (QPOs) of test particles near stable circular orbits, including the precession effects such as periastron precession and the Lense-Thirring effect. We compare our results with those corresponding to the Kerr BH. We find that the particle motion is strongly shaped by the BH parameters. Using a WKB approach, we also study scalar quasinormal modes of rotating KBR BH in an external magnetic field and show that the magnetic field increases damping, while rotation and angular momentum mainly set the oscillation frequencies. Alternatively, general relativistic modeling of Bondi-Hoyle-Lyttleton (BHL) accretion onto rapidly rotating KBR BH shows that two distinct physical structures emerge and cyclically transform into one another over time. These processes produce either a strongly oscillating flip-flop shock cone or a nearly stationary toroidal structure, with their formation governed by the BH spin and magnetic curvature. Power spectral analysis shows that these configurations give rise to low- and high-frequency QPO, providing a unified theoretical framework to understand how multiple QPO-like features can arise in rapidly spinning accreting systems.

gr-qc↗

arXiv2026

Joule-Thomson Effect and Geodesic Structure of Charged AdS Black Holes in f(R,T) Coupled with Nonlinear Electrodynamics

We herein study both the Joule-Thomson (JT) expansion process and the geodesic properties of a charged anti-de Sitter (AdS) black hole arising in modified gravity with nonlinear electrodynamic (NLED) sources. Our thermodynamic study reveals that the black hole charge has the most pronounced impact on the JT behaviour. The nonlinear electromagnetic sector together with the modified gravity parameters introduces further corrections to the inversion temperature and the associated cooling characteristics. At astrophysically relevant distances, the geometry closely reproduces expected outcomes.

gr-qc↗

arXiv2026

Thermodynamic Geometry, Heat Engines, and Topology of Sharma--Mittal ModMax-dRGT Black Holes

We investigate the thermodynamic structure of charged AdS black holes in ModMax nonlinear electrodynamics coupled to dRGT-like massive gravity, incorporating Sharma--Mittal entropy corrections. The thermodynamic geometry is analyzed using the Weinhold metric in the parameter space spanned by the horizon radius and electric charge. The resulting thermodynamic Ricci scalar characterizes effective microscopic interactions, with curvature singularities signaling extremal boundaries and degeneracies of the thermodynamic metric. We further construct a rectangular black hole heat engine in the extended phase space and derive an exact expression for its efficiency, demonstrating how the ModMax parameter and massive-gravity couplings influence the enthalpy-based conversion of heat into work, while the Sharma--Mittal parameters modify the Carnot bound through corrections to the black-hole temperature. Finally, a topological analysis of the corrected temperature and generalized free energy reveals both conventional and novel critical points, and the associated conserved topological charge is investigated.

gr-qc↗

arXiv2026

Extended Thermodynamics and Throttling Process of Charged AdS Black Holes in ModMax-dRGT Massive Gravity with Sharma-Mittal Entropy

We investigate the extended thermodynamics, including the Joule-Thomson expansion and $P-V$ criticality, of a four-dimensional charged anti-de Sitter (AdS) black hole within the combined framework of ModMax nonlinear electrodynamics and dRGT-like massive gravity. Operating in the extended phase space and employing the generalised Sharma-Mittal entropy to account for non-extensive statistical correlations, we derive exact analytical expressions for the modified Hawking temperature, specific heat, Joule-Thomson coefficient, and the equation of state. Our analysis of the throttling process reveals that the conformal nonlinearities of the ModMax field ($γ$) expand the physically accessible cooling domain by shifting the inversion transition to smaller horizon radii. While the Sharma-Mittal parameters ($δ$, $R$) critically govern local thermodynamic stability and the inversion radius, the global inversion phase boundary remains fundamentally dictated by the massive graviton background. Furthermore, an analysis of the Gibbs free energy uncovers a van der Waals-like first-order phase transition characterized by a distinct swallow-tail structure. We observe a clear physical decoupling in the critical regime: ModMax nonlinearities modify the critical phase boundary by suppressing electromagnetic interactions, Sharma-Mittal parameters dictate the relative thermal stability of competing phases, and massive gravity governs the overarching macroscopic phase landscape. These results highlight the sensitivity of thermodynamic phase phenomena as robust diagnostic tools for distinguishing nonlinear and non-extensive modifications to black hole physics.

gr-qc↗

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

Impact of Thermodynamic Corrections on the Stability of Hayward-Anti de Sitter Black Hole Surrounded by a Fluid of Strings

We explore the modified thermodynamics of a Hayward-Anti de Sitter (H-AdS) black hole in atypical conditions, incorporating a string fluid, Hayward regularisation, and quantum entropy corrections. Our analysis reveals a first-order phase transition between small and large black hole phases, characterised by a swallowtail behaviour in the Gibbs free energy profiles. It is found that the key parameters - string fluid strength, Hayward regularisation scale, and quantum correction coefficients significantly influence the critical temperature and phase stability of the H-AdS system. It is further noticed that a large black hole phase is stabilised by these modifications, with quantum corrections smoothing the transition. This model offers a valuable framework to study quantum gravity effects on black hole thermodynamics with potential implications in analysing black hole evolution and astrophysical observations.

gr-qc↗

arXiv2025

Accretion Disk Luminosity and Topological Characteristics for a Schwarzschild Black Hole Surrounded by King Dark Matter Halo

This study delves into the intricate properties of a Schwarzschild black hole enveloped by King dark matter in an isotropic configuration. The thermodynamic characteristics of this black hole are meticulously analyzed, and the dynamics of massive and massless particles in its vicinity are investigated. In examining the trajectories of massless particles, the shadow cast in the presence of King dark matter is explored, revealing virtual ranges for the corresponding parameters. For the dynamics of massive particles, the radius of the innermost stable circular orbit, angular momentum, energy, and angular velocity of a test particle within the King dark matter framework surrounding the black hole are calculated. The effect of King dark matter on the accretion disk energy flux, effective radiation temperature, differential luminosity, and spectral luminosity are then investigated. The stability of the photon sphere in the presence of King dark matter is also studied, and finally, the thermodynamic potentials of this black hole are examined from a topological perspective.

gr-qc↗

arXiv2025

Investigating Optical and Ring-Down Gravitational Wave Properties of a Rotating Black Hole in a Dehnen Galactic Dark Matter Halo

We present a comprehensive study of the optical and dynamical properties of a rotating black hole immersed in a Dehnen-type $(1,4,0)$ galactic dark matter halo, modeled by a double power-law density profile commonly used to describe realistic galactic cores. By extending our previous Schwarzschild-Dehnen solution using a modified Newman-Janis algorithm, we construct a Kerr-like axisymmetric spacetime that smoothly incorporates both black hole rotation and the influence of the surrounding dark matter halo. We systematically investigate the effects of the halo parameters-the central density and halo radius-on horizon structure, the shape and extent of the ergoregion, and the null geodesics associated with black hole shadows. Our results show that the presence of a dense or extended halo expands the event horizon and ergoregion, and significantly alters the size and distortion of the black hole shadow. Furthermore, by applying the WKB approximation to scalar field perturbations, we compute the quasinormal mode (QNM) spectra and demonstrate that the frequencies and damping times of ringdown signals are highly sensitive to the halo profile. These results open promising avenues for probing the dark matter environment of astrophysical black holes through black hole imaging and gravitational wave observations.

astro-ph.CO↗