arXiv subjects

Neeraj Pant

Publications and source records attributed to Neeraj Pant.

8 recordsLinked to original sources

arXiv2020

A new class of viable and exact solutions of EFE's with Karmarkar conditions: An application to cold star modeling

In this work we present a theoretical framework within Einstein's classical general relativity which models stellar compact objects such as PSR J1614-2230 and SAX J1808.4-3658. The Einstein field equations are solved by assuming that the interior of the compact object is described by a class I spacetime. The so-called Karmarkar condition arising from this requirement is integrated to reduce the gravitational behaviour to a single generating function. By appealing to physics we adopt a form for the gravitational potential which is sufficiently robust to accurately describe compact objects. Our model satisfies all the requirements for physically realistic stellar structures.

gr-qc↗

arXiv2019

Generating functions of wormholes

It is known that wormhole geometry could be found solving the Einstein field equations by tolerating the violation of null energy condition (NEC). Violation of NEC is not possible for the physical matter distributions, however, can be achieved by considering distributions of "exotic matter". The main purpose of this work is to find generating functions comprising the wormhole like geometry and discuss the nature of these generating functions. We have used the Herrera et al. \cite{1} approaches of obtaining generating functions in the background of wormhole spacetime. Here we have adopt two approaches of solving the field equations to find wormhole geometry. In the first method, we have assumed the redshift function $f(r)$ and the shape function $b(r)$ and solve for the generating functions. In an another attempt we assume generating functions and redshift functions and then try to find shape functions of the wormholes.

physics.gen-ph↗

arXiv2017

A charged anisotropic well-behaved Adler-Finch-Skea solution Satisfying Karmarkar Condition

In the present article, we discover a new well-behaved charged anisotropic solution of Einstein-Maxwell's field equations. We ansatz the metric potential $g_{00}$ of the form given by Maurya el al. (arXiv:1607.05582v1) with $n=2$. In their article it is mentioned that for $n=2$ the solution is not well-behaved for neutral configuration as the speed of sound is non-decreasing radially outward. However, the solution can represent a physically possible configuration with the inclusion of some net electric charged i.e. the solution can become a well-behaved solution with decreasing sound speed radially outward for a charged configuration. Due to the inclusion of electric charged the solution leads to a very stiff equation of state (EoS) with the velocity of sound at the center $v_{r0}^2=0.819, ~v_{t0}^2=0.923$ and the compactness parameter $u=0.823$ is closed to the Buchdahl limit 0.889. This stiff EoS support a compact star configuration of mass $5.418M_\odot$ and radius of $10.1 km$.

physics.gen-ph↗

arXiv2017

Physical viability of fluid spheres satisfying the Karmarkar condition

We obtain a new solution of the TOV-equation for an anisotropic fluid distribution by imposing the Karmarkar condition. In order to close the system of equations we postulate an interesting form for the grr gravitational potential which allows us to solve for gtt metric component via the Karmarkar condition. We demonstrate that the new interior solution has well-behaved physical attributes and can be utilized to model relativistic static fluid spheres. By using observational data sets for the radii and mass-to-radius relations for compact stars such as 4U 1538-52, LMC X-4 and PSR J1614- 2230 we show that our solution describes these objects to a very good degree of accuracy. The physical plausibility of the solution depends on a parameter $c$ for a particular star. For 4U 1538-52 the solution behaves well for $0.1574 \le c \le 0.46$ which corresponds to $1 \ge v^2_{r0} \ge 0:13$, $0.91 \ge v^2_{t0}\ge 0.04$ and $17.8 \ge Γ_0 \ge 3.8$. For LMC X-4 the solution behaves well for $0.1235 \le c \le 0.35$ which corresponds to $0.99 \ge v^2_{r0} \ge 0.15$, $0.91 \ge v^2_{t0}\ge 0.06$ and $15.35 \ge Γ_0 \ge 3.35$. Our model approximates the pulsar PSR J1614-2230 for $0.05 \le c \le 0.13$ which corresponds to $1 \ge v^2_{r0}\ge 0.21$, $0.94 \ge v^2_{t0} \ge 0.13$ and $8.34 \ge Γ_0 \ge 2.34$. Our observations of the behavior of the thermodynamical and physical variables of these compact objects lead us to conclude that the parameter c plays an important role in determining the equation of state of the stellar material. It is apparent that smaller values of c lead to stiffer equation of states and vice-versa.

gr-qc↗

arXiv2016

Anisotropic compact stars in Karmarkar spacetime

We present a new class of solutions to the Einstein field equations for an anisotropic matter distribution in which the interior space-time obeys the Karmarkar condition. The necessary and sufficient condition required for a spherically symmetric space-time to be of class one reduces the gravitational behavior of the model to a single metric function. By assuming a physically viable form for the $g_{rr}$ metric potential we obtain an exact solution of the Einstein field equations which is free from any singularities and satisfies all the physical criteria. We utilize this solution to predict the masses and radii of well-known compact objects such as Cen X-3, PSR J0348+0432, PSRB0943+10 and XTE J1739-285. To be publish in Chinese Physics C (Accepted)

physics.gen-ph↗

arXiv2016

A family of well-behaved Karmarkar spacetime describing interior of relativistic stars

We are presenting a family of new exact solutions for relativistic anisotropic stellar objects by considering four dimensional spacetime embedded in five dimensional Pseudo Euclidean space known as Class I solutions. These solutions are well-behaved in all respects, satisfy all energy conditions and the resulting compactness parameter is also within Buchdahl limit. The well-behaved nature of the solutions for a particular star solely depends on index n. We have discussed the solutions in detail for the neutron star XTE J1739-285 (M = 1.51M$\odot$, R = 10.9 km). For this particular star, the solution is well behaved in all respects for $8 \le n \le 20$. However, the solutions with n < 8 possess increasing trend of sound speed and the solutions belong to n > 20 disobey causality condition. Further, the well-behaved nature of the solutions for PSR J0348+0432 (2.01M$\odot$, 11 km), EXO 1785-248 (1.3M$\odot$, 8.85 km) and Her X-1 (0.85M$\odot$, 8.1 km) are specified by the index n with limits $24 \le n \le 54$, $1.5 \le n \le 4$ and $0.8 \le n \le 2.7$ respectively.

physics.gen-ph↗

arXiv2016

A new solution of embedding class I representing anisotropic fluid sphere in general relativity

In the present paper we are willing to model anisotropic star by choosing a new grr metric potential. All the physical parameters like the matter density, radial and transverse pressure and are regular inside the anisotropic star, with the speed of sound less than the speed of light. So the new solution obtained by us gives satisfactory description of realistic astrophysical compact stars. The model of the present paper is compatible with observational data of compact objects like RX J1856-37, Her X-1, Vela X-12 and Cen X-3. A particular model of Her X-1 (Mass 0.98 times solar mass and radius=6.7 km.) is studied in detail and found that it satisfies all the condition needed for physically acceptable model. Our model is described analytically as well as with the help of graphical representation.

gr-qc↗

arXiv2014

Anisotropic fluid star model in isotropic coordinates

We present a spherically symmetric solution of the general relativistic field equations in isotropic coordinates for anisotropic neutral fluid, compatible with a super dense star modeling by considering a specific choice of anisotropy factor that includes a positive constant defined as anisotropy parameter, which varies the relation between the radial and tangential pressure. Further, we have constructed a super-dense star model with all degree of suitability. We have found that the maximum mass decreases with the increase of anisotropy parameter. The robustness of our result is that it matches with the recent discoveries.

gr-qc↗