arXiv subjects

Sushant G Ghosh

Publications and source records attributed to Sushant G Ghosh.

7 recordsLinked to original sources

arXiv2026

Gravitational Wave Signatures from Periodic Orbits around a non-commutative inspired black hole surrounded by quintessence

We study gravitational wave emission from periodic orbits of a test particle around a noncommutative-inspired black hole surrounded by quintessence. Using the zoom-whirl taxonomy, which is characterized by three topological numbers $(z, w, v)$, we classify these orbits and calculate several representative gravitational waveforms for certain periodic orbits. We find that the noncommutative parameter $Θ$ and the quintessence field significantly modify both the orbital structure and the emitted waveforms. In particular, increasing $Θ$ leads to a phase shift and a change in amplitude in the waveform, while higher zoom numbers produce more complicated substructures. The characteristic strain spectra peak in the millihertz range, lying within the sensitivity band of the LISA detector. Moreover, the presence of the quintessence field introduces significant modifications to these waveforms, imprinting measurable deviations that could be tested or constrained by future space-based gravitational wave detectors. These results suggest that future space-based gravitational wave missions could probe or constrain noncommutative effects in strong gravitational fields.

gr-qc↗

arXiv2025

Signatures of Quantum-Corrected Black Holes in Gravitational Waves from Periodic Orbits

We investigate gravitational wave emission from periodic timelike orbits of a test particle around a loop quantum gravity-inspired Schwarzschild black hole. The spacetime is characterised by a holonomy-correction parameter that modifies the radial metric component while preserving asymptotic flatness and the classical location of the horizon. The bound geodesics are systematically classified using the zoom--whirl representation labelled by three integers $(z,w,v)$. Gravitational waveforms are computed within a numerical framework that combines exact geodesic motion with the quadrupole approximation, which is suitable for extreme mass ratio inspirals. We demonstrate that the quantum corrections lead to distinct phase shifts, amplitude variations, and modifications to the harmonic structure of the waveforms, with increasingly complex features for orbits with larger zoom numbers. The corresponding frequency spectra and characteristic strain peak, which fall within the millihertz band, are within the sensitivity ranges of space-based detectors such as LISA, Taiji, and TianQin. For specific orbital configurations and values of the quantum-correction parameter, the characteristic strain exceeds the projected detector noise, indicating potential observability. Our results demonstrate that gravitational waves from periodic orbits provide a sensitive probe of quantum-corrected black hole spacetimes in the strong-field regime.

gr-qc↗

arXiv2022

Testing Rotating Regular Metrics with EHT Results of Sgr A*

The Event Horizon Telescope (EHT) observation unveiled the first image of supermassive black hole Sgr A* showing a shadow of diameter $θ_{sh}= 48.7 \pm 7\,μ$as with fractional deviation from the Schwarzschild black hole shadow diameter $δ= -0.08^{+0.09}_{-0.09}~\text{(VLTI)},-0.04^{+0.09}_{-0.10}~\text{(Keck)}$. The Sgr A* shadow size is within $~10\%$ of the Kerr predictions, providing us with another tool to investigate the nature of strong-field gravity. We use the Sgr A* shadow observables to constrain metrics of four independent and well-motivated, parametrically different from Kerr spacetime, rotating regular spacetimes, and the corresponding no-horizon spacetimes. We present constraints on the deviation parameter $g$ of rotating regular black holes. The shadow angular diameter $θ_{sh}$ within $1 σ$ region, places bounds on the parameters $a$ and $g$. Together with EHT bounds on $θ_{sh}$ and $δ$ of Sgr A*, our analysis concludes that the three rotating regular black holes, viz., Bardeen Hayward, and Simpson-Visser black holes, and corresponding no-horizon spacetimes agree with the EHT results of Sgr A*. Thus, these three rotating regular spacetimes and Kerr black holes are indiscernible in some parameter space, and one can not rule out the possibility of the former being strong candidates for astrophysical black holes.

gr-qc↗

arXiv2022

Thermodynamics and phase transition of rotating regular-de Sitter black holes

We analyze thermodynamic properties of the rotating regular black holes having mass ($M$), angular momentum ($a$), and a magnetic charge $(g)$, and encompass Kerr black hole ($g=0$). The mass $M$ has a minimum at the radius $r_+=r_+^{\star}$, where both the heat capacity and temperature vanish. The thermal phase transition is because of the divergence of heat capacity at a critical radius $r_{+}^C$ with stable (unstable) branches for $r_+ r_+^C$). We also generalize the rotating regular black holes in de Sitter (dS) background and analyzed its horizon structure to show that for each $g$, there are two critical values of the mass parameter $M_{\text{cr1}}$ and $M_{\text{cr2}}$ which correspond to the degenerate horizons. Thus, we have rotating regular-dS black holes with an additional cosmological horizon apart from the inner (Cauchy) and the outer (event) horizons. Next, we discuss the effective thermodynamic quantities of the rotating regular-dS black holes in the extended phase space where the cosmological constant ($Λ$) is considered as thermodynamic pressure. Combining the first laws at the two horizons, we calculate the heat capacity at constant pressure $C_P$, the volume expansion coefficient $α$, and the isothermal compressibility $κ_T$. At a critical point, the specific heat at constant pressure, the volume expansion coefficient, and the isothermal compressibility of the regular-dS black holes exhibit an infinite peak suggesting a second-order phase transition.

gr-qc↗

arXiv2020

5D rotating regular Myers-Perry black holes and their shadow

It is widely believed that the curvature singularities are an artifact of general relativity and may not exist in the Universe, and likely to be defined by the quantum gravity. In the absence of successful quantum gravity, significant attention has been shifted towards the regular models. We present a five-dimensional ($5D$) rotating regular Myers-Perry like black hole metric with two rotation parameters ($a,b$) and a free parameter ($k$). Our $5D$ rotating regular metric encompasses $5D$ Myers-Perry black hole which can be recovered as a special case when $k=0$. The size of the shadow cast by the black holes is significantly smaller and more distorted when the parameter $k$ is increased.

gr-qc↗

arXiv2014

Thermodynamic structure of field equations near apparent horizon for radiating black holes

We study the intriguing analogy between gravitational dynamics of the horizon and thermodynamics for the case of nonstationary radiating spherically symmetric black holes both in four dimensions and higher dimensions. By defining all kinematical parameters of nonstationary radiating black holes in terms of null vectors, we demonstrate that it is possible to interpret the Einstein field equations near the apparent horizon in the form of a thermodynamical identity $TdS=dE+PdV$.

gr-qc↗

arXiv2014

Spinning Higher Dimensional Einstein-Yang-Mills black holes

We construct a Kerr-Newman-like spacetimes starting from higher dimensional (HD) Einstein-Yang-Mills black holes via complex transformations suggested by Newman-Janis. The new metrics are HD generalization of Kerr-Newman spacetimes which has a geometry precisely that of Kerr-Newman in 4D corresponding to Yang-Mills (YM) gauge charge, but the sign of charge term gets flipped in the HD spacetimes. It is interesting to note that gravitational contribution of YM gauge charge, in HD, is indeed opposite (attractive rather than repulsive) that of Maxwell charge. The effect of YM gauge charge on the structure and location of static limit surface and apparent horizon is discussed. We find that static limit surfaces become less prolate with increase in dimensions and are also sensitive to YM gauge charge thereby affecting the shape of ergosphere. We also analyze some thermodynamical properties of these BHs.

gr-qc↗