arXiv subjects

Parangam Goswami

Publications and source records attributed to Parangam Goswami.

4 recordsLinked to original sources

arXiv2023

Traversable wormholes in $f(R)$ gravity sourced by a cloud of strings

Wormhole solutions in General Relativity (GR) require \textit{exotic} matter sources that violate the null energy condition (NEC), and it is well known that higher-order modifications of GR and some alternative matter sources can support wormholes. In this study, we explore the possibility of formulating traversable wormholes in $f(R)$ modified gravity, which is perhaps the most widely discussed modification of GR, with two approaches. First, to investigate the effects of geometrical constraints on the global characteristics, we gauge the $rr$-component of the metric tensor, and employ Padè approximation to check whether a well-constrained \textit{shape function} can be formulated in this manner. We then derive the field equations with a background of string cloud, and numerically analyse the energy conditions, stability, and amount of exotic matter in this space-time. Next, as an alternative source in a simple $f(R)$ gravity model, we use the background cloud of strings to estimate the wormhole shape function, and analyse the relevant properties of the space-time. These results are then compared with those of wormholes threaded by normal matter in the simple $f(R)$ gravity model considered. The results demonstrate that wormholes with NEC violations are feasible; however, the wormhole space-times in the simple $f(R)$ gravity model are unstable.

gr-qc↗

arXiv2023

Spherically symmetric wormholes in General Relativity and modified gravity with a Kalb-Ramond background

Among the several modified/extended gravity paradigms, the concept of antisymmetric connections leading to space-time torsion can be traced back to Cartan. More recently, developments in string theory have suggested the existence of a rank-2 self-interacting tensor field called the Kalb-Ramond field with similar outcomes, the field strength of which can support analytic wormhole-like solutions. However, detailed analyses of the physical properties of interest of such solutions are lacking. In this study, we comprehensively probe the properties of traversable Morris-Thorne like wormhole solutions sourced by the Kalb-Ramond field strength in both General Relativity (GR) and $f(R)$ and $f(R,T)$ modified gravity. We also analyze the coupling of the field strength in GR via a novel non-minimal interaction term in the action. Using suitable parametric constraints in all cases, we evaluate wormhole shape functions, numerically analyze the energy conditions near the throat, check the stability using the generalized Tolman-Oppenheimer-Volkov equation, and demonstrate the possibility of minimum exotic matter by estimating the volume integral quantifier. Our results show the existence of stable wormhole solutions in GR and a simple $f(R,T)$ gravity model, and unstable ones in a power-law type $f(R)$ gravity model.

gr-qc↗

arXiv2022

New Wormhole Solutions in a Viable $f(R)$ Gravity Model

Traversable wormhole solutions in General Relativity require exotic matter sources that violate the null energy condition (NEC), and such behavior maybe avoided in modified gravity. In this study, we analyze the energy conditions for static, spherically symmetric traversable Morris-Thorne wormholes in a recently proposed viable $f(R)$ gravity model. We numerically analyze solutions considering both constant and variable redshift functions, and present wormhole space-times respecting the NEC, supported by a phantom energy-like equation of state for the source. Moreover, we analyze the stability of the space-times using the generalized Tolman-Oppenheimer-Volkov equation. We demonstrate the effects of certain parameters in the $f(R)$ model in determining energy condition violations, and establish that stable wormholes can be formulated only at the expense of violating the NEC.

gr-qc↗

arXiv2022

Non-commutative Wormholes in $f(R)$ Gravity satisfying the Energy Conditions

Traversable wormholes in General Relativity (GR) require exotic matter sources that violate the null energy condition (NEC), and such behavior may be avoided in modified gravity. Moreover, the concept of non-commutative geometry as a gravitational source can be leveraged both in GR and modified gravity to realize non-trivial space-time configurations. In this study, we use $f(R)$ gravity in conjunction with non-commutative geometry to analyze spherically symmetric traversable Morris-Thorne wormhole solutions from the aspect of energy condition violation, considering both constant and variable red-shift functions. First, we use well constrained metric and model parameters in a viable $f(R)$ gravity model to demonstrate that wormholes respecting the NEC can be obtained with suitable choices of parameters. Additionally, we check the strong and dominant energy conditions to further validate our results. We then leverage non-commutative geometry in the framework of $f(R)$ gravity to show that wormholes respecting the different energy conditions with a phantom-like source can be realized with suitable choices of model parameters. Our comprehensive analyses using well-constrained model parameters show that wormholes satisfying the NEC can be realized in the framework of non-commutative geometry with modified gravity.

gr-qc↗