arXiv subjects

Bibhash Das

Publications and source records attributed to Bibhash Das.

3 recordsLinked to original sources

arXiv2025

Spherical accretion onto higher-dimensional Reissner-Nordstr\"{o}m Black Hole

We obtain relativistic solutions of spherically symmetric accretion by a dynamical analysis of a generalised Hamiltonian for higher-dimensional Reissner-Nordstr\"{o}m (RN) Black Hole (BH). We consider two different fluids namely, an isotropic fluid and a non-linear polytropic fluid to analyse the critical points in a higher-dimensional RN BH. The flow dynamics of the fluids are studied in different spacetime dimensions in the framework of Hamiltonian formalism. The isotropic fluid is found to have both transonic and non-transonic flow behaviour, but in the case of polytropic fluid, the flow behaviour is found to exhibit only non-transonic flow, determined by a critical point that is related to the local sound speed. The critical radius is found to change with the spacetime dimensions. Starting from the usual four dimensions it is noted that as the dimension increases the critical radius decreases, attains a minimum at a specific dimension ($D>4$) and thereafter increases again. The mass accretion rate for isotropic fluid is determined using Hamiltonian formalism. The maximum mass accretion rate for RN BH with different equations of state parameters is studied in addition to spacetime dimensions. The flow behaviour and mass accretion rate for a change in BH charge is also studied analytically. It is noted that the maximum mass accretion rate in a higher-dimensional Schwarzschild BH is the lowest, which however, increases with the increase in charge parameter in a higher-dimensional RN BH.

gr-qc↗

arXiv2025

A study of the pulsar EXO 1745-248 in $f(Q)$ gravity with pseudo-spheroidal geometry

We present a singularity-free relativistic interior solution for constructing stable quark stellar models in the framework of a linear $f(Q)$ gravity ($f(Q) = \alpha Q + \phi$) satisfying the pseudo-spheroidal geometry. The physical features and the stability of the stellar model is explored with strange star (SS) candidate EXO 1745-248 ($M = 1.7\, M_{\odot}$ and $R = 9\, km$). The Durgapal-Banerjee transformation is employed to obtain the relativistic interior solution using the MIT Bag model equation of state (EoS): $P = \frac{1}{3}(\rho - 4 B_{g})$. For a linear form of $f(Q)$ gravity, we obtain the exterior vacuum solution, which reduces to the Schwarzschild-de Sitter (SdS) solution with the cosmological constant term, $\Lambda = \frac{\phi}{2\alpha}$. The stellar model is analyzed for the different values of the spheroidicity parameter ($\mu$). The value of $\alpha$ is constrained using a viable physical limit on the Bag parameter ($B_{g} \in [57.55,95.11]\,MeV\,fm^{-3}$). The constraints on Mass-Radius relation indicates that physically acceptable SS models are permitted for $\mu \geq 7$. The contribution of $\mu$ to the energy density, pressure profiles, and other physical features is studied for the SS candidate EXO 1745-248. The stability of the stellar model obtained here is also analyzed through causality condition, adiabatic index and other stability criteria. We also investigate the stellar model for other SS candidates to test its viability. The relativistic interior solution obtained here can be used to construct viable and physically acceptable strange star models with very high compactness ratio in the framework of linear $f(Q)$ gravity.

gr-qc↗

arXiv2025

Wormholes in 4D Einstein-Gauss-Bonnet gravity with BEC Dark Matter density profile

The existence of Traversable Wormhole (TW) in the 4D Einstein-Gauss-Bonnet (4D-EGB) gravity is explored with phenomenological Bose-Einstein Condensates (BEC) dark matter density profile. In the framework of 4D EGB gravity, which one obtains by regularizing the higher-dimensional EGB gravity in the limit $D \to 4$ is considered to obtain a spherically symmetric TW. The Gauss-Bonnet coupling parameter ($\alpha$) in this case is rescaled to $\alpha \to \frac{\alpha}{D-4}$. Considering the energy density profile of non-relativistic BEC matter, the shape function of the WH geometry and the Null energy condition (NEC) are determined with a constant redshift function. The applicability of realistic flaring-out condition and asymptotic flatness conditions are studied here and the domain of model parameters for realistic scenario is determined. We analyze the embedding diagram of the WH obtained here with proper radial distance, volume integral quantifier, and anisotropy. We obtained WH which is stable at the throat when $\alpha = -0.0512471$ for a set of model parameters, which is estimated from sound speed measurement. The energy conditions are investigated, and it is noted that there is a range of Gauss-Bonnet coupling parameter $\alpha \in [-4,-4.222]$, at which the energy conditions, including NEC, are obeyed at the throat. We explore NEC for other values of $\alpha$ and found that it is not satisfied. The other energy conditions are also violated. A new result is thus obtained with 4D Einstein-Gauss-Bonnet gravity with BEC Dark Matter profile. We determine the parameter space for which the WH solution exists in the proposed modified gravity model.

gr-qc↗