arXiv subjects

Anjan Kar

Publications and source records attributed to Anjan Kar.

6 recordsLinked to original sources

arXiv2026

Gravitational wave radiation from periodic orbits in regular black holes

Gravitational wave radiation from periodic orbits in some standard regular black hole spacetimes is studied, primarily using known methods (numerical and analytic). We demonstrate specific differences with the singular Schwarzschild geometry by analysing orbit characteristics, gravitational wave strain profiles, and the corresponding power spectrum density, for different values of the regularising parameter `$g$'. Further, we assess our results vis-a-vis the LISA sensitivity curves and show how our results may be useful while developing templates for detecting regular black holes as viable alternatives to the singular ones. The appendices to our article contain details on errors in our estimates and provide for the first time, some exact analytical expressions on gravitational wave radiation from different types of periodic orbits in Schwarzschild spacetime.

gr-qc↗

arXiv2025

A note on the Penrose process in rotating regular black holes

We investigate the Penrose process of energy extraction in the context of rotating regular black holes. For the Neves-Saa class of regular black hole solutions, which includes the Bardeen, Hayward and Fan-Wang spacetimes as special cases, the extraction efficiency is bounded above by the known value for Kerr spacetime. However, in the case of a new rotating regular black hole which does not have a Schwarzschild singular limit for zero rotation, the extraction efficiency can indeed become very large, as shown in our analysis here.

gr-qc↗

arXiv2025

Diverse regular spacetimes using a parametrised density profile

We explore the construction of diverse regular spacetimes (black holes and defects) in General Relativity (GR) using a generic parametrised density profile (the Dekel-Zhao profile), which includes, for specific parameter choices, various well-known examples usually studied in the context of dark matter halos. Our solutions, in the Schwarzschild gauge, include new regular black holes as well as non-singular solutions representing spacetime defects. For a sub-class of metrics, a TOV equation approach with a chosen equation of state works. The status of the energy conditions and the issue of geodesic completeness are explored in detail. We also provide possible Lagrangian density constructions for the matter energy-momentum tensors. Further, we study the shadow radius of the new regular black holes, and compare our findings with available observational results from the EHT collaboration. Finally, for the defect solution, we present a model for a stable star (a gravastar) by explicit use of the junction conditions and obtain relevant consequences highlighting its characteristic features.

gr-qc↗

arXiv2024

New rotating Lorentzian wormhole spacetime

A rotating version of a known static, spherically symmetric, zero Ricci scalar Lorentzian wormhole is constructed. It turns out that for this given non-rotating geometry, the standard Newman-Janis algorithm does not produce a rotating wormhole and, therefore, the method pioneered by Azreg-A\"inou has to be used. The rotating spacetime thus obtained is shown to be regular with wormhole features, though it is no longer a $R=0$ spacetime. The required matter is found to violate the energy conditions, as expected. A few other characteristic properties of this new rotating spacetime are mentioned. Finally, we calculate the shadow for this geometry and discuss its features {\em vis-a-vis} the Kerr geometry and available event horizon telescope observations.

gr-qc↗

arXiv2024

Aspects of a novel nonlinear electrodynamics in flat spacetime and in a gravity-coupled scenario

A novel nonlinear electrodynamics (NLE) model with two dimensionful parameters is introduced and investigated. Our model obeys the Maxwellian limit and exhibits behaviour similar to the Born-Infeld Lagrangian in the weak field limit. It is shown that the electric field of a point charge in this model has a definite maximum value. Thus, the self-energy of the point charge is finite. The phenomenon of vacuum birefringence is found to occur in the presence of an external uniform electric field. Causality and unitarity conditions for all background electric fields hold, whereas, for magnetic fields, a restricted domain of validity is found. Moreover, a minimal coupling of Einstein's General Relativity (GR) with this NLE results in solutions of regular black holes or naked singularities, depending on whether the source is a nonlinear magnetic monopole or an electric charge, respectively.

gr-qc↗

arXiv2023

Novel regular black holes: geometry, source and shadow

We propose a two-parameter, static and spherically symmetric regular geometry, which, for specific parameter values represents a regular black hole. The matter required to support such spacetimes within the framework of General Relativity (GR), is found to violate the energy conditions, though not in the entire domain of the radial coordinate. A particular choice of the parameters reduces the regular black hole to a singular, mutated Reissner-Nordstrom geometry. It also turns out that our regular black hole is geodesically complete. Fortunately, despite energy condition violation, we are able to construct a viable source, within the framework of GR coupled to matter, for our regular geometry. The source term involves a nonlinear magnetic monopole in a chosen version of nonlinear electrodynamics. We also suggest an alternative approach towards constructing a source, using the effective Einstein equations which arise in the context of braneworld gravity. Finally, we obtain the circular shadow profile of our regular black hole and provide a preliminary estimate of the metric parameters using recent observational results from the EHT collaboration.

gr-qc↗