arXiv subjects

Saibal Ray

Publications and source records attributed to Saibal Ray.

At least 109 records · Page 6Linked to original sources

arXiv2016

The Finslerian wormhole models

We present models of wormhole under the Finslerian structure of spacetime. This is a sequel of our previous work (Eur Phys J 75:564, 2015) where we constructed a toy model for compact stars based on the Finslerian spacetime geometry. In the present investigation, a wide variety of solutions are obtained that explore wormhole geometry by considering different choices for the form function and energy density. The solutions, like the previous work, are revealed to be physically interesting and viable models for the explanation of wormholes as far as the background theory and literature are concerned.

gr-qc↗

arXiv2016

Generalized model for anisotropic compact stars

In the present investigation an exact generalized model for anisotropic compact stars of embedding class one is sought for under general relativistic background. The generic solutions are verified by exploring different physical aspects, viz. energy conditions, mass-radius relation, stability of the models, in connection to their validity. It is observed that the model present here for compact stars is compatible with all these physical tests and thus physically acceptable as far as the compact star candidates $RXJ~1856-37$, $SAX~J~1808.4-3658~(SS1)$ and $SAX~J~1808.4-3658~(SS2)$ are concerned.

physics.gen-ph↗

arXiv2016

Kantowski-Sachs Universe in the Varying Speed of Light Theory

In this work we consider the Kantowski-Sachs (KS) universe in the framework of varying speed of light theory. We present the general solutions of the gravitational field equations with variable speed of light $c(t)$, gravitational coupling parameter $G(t)$ and the decaying vacuum energy $Λ(t)$ for the KS model. In the limiting case for the equation of state (EOS) parameter $γ=2$ (stiff fluid with $p=ρc^2$) and $γ=1$ (dust with $p=0$), exact solutions of the field equations are obtained. The numerical solutions are also presented for both the cases. Moreover, it is shown that in the limiting case of large time, the mean anisotropy parameter tends to zero for $γ=2$ and $γ=1$. Thus the time variation of the fundamental constants provides an effective mechanism for the isotropization of the KS universe.

physics.gen-ph↗

arXiv2016

A new model for spherically symmetric charged compact stars of embedding class one

In the present study we search for a new stellar model with spherically symmetric matter and charged distribution under general relativistic framework. The model represents a compact star of embedding class one. The solutions obtain here are general in their nature having the following two features: firstly, the metric becomes flat and also the expressions for the pressure, energy density and electric charge become zero in all the cases if we consider the constant $A=0$, which shows that our solutions represent the so-called `electromagnetic mass model' \cite{Lorentz1904}, and secondly, the metric function $ν(r)$, for the limit $n$ tends to infinity, converts to $ν(r)=C{r}^{2}+ ln~B$, which is the same as considered by Maurya et al. \cite{Maurya2015a}. We have investigated several physical aspects of the model and find that all the features are acceptable within the demand of the contemporary theoretical studies and observational evidences.

gr-qc↗

arXiv2016

A new model for spherically symmetric anisotropic compact star

In this article we obtain a new anisotropic solution for Einstein's field equation of embedding class one metric. The solution is representing the realistic objects such as $Her~X-1$ and $RXJ~1856-37$. We perform detailed investigation of both objects by solving numerically the Einstein field equations under with anisotropic pressure. The physical features of the parameters depend on the anisotropic factor i.e. if anisotropy is zero everywhere inside the star then the density and pressures will become zero and metric turns out to be flat. We report our results and compare with the above mentioned two compact objects on a number of key aspects: the central density, the surface density onset and the critical scaling behavior, the effective mass and radius ratio, the anisotropization with isotropic initial conditions, adiabatic index and red shift. Along with this we have also made a comparison between the classical limit and theoretical model treatment of the compact objects. Finally we discuss the implications of our findings for the stability condition in relativistic compact star.

physics.gen-ph↗

arXiv2016

Charged Perfect Fluid Sphere in Higher Dimensional Spacetime

Present paper provides a new model for perfect fluid sphere filled with charge in higher dimensional spacetime admitting conformal symmetry. We consider a linear equation of state with coefficients fixed by the matching conditions at the boundary of the source corresponding to the exterior Reissner-Nordström higher dimensional spacetime. Several physical features for different dimensions, starting from four up to eleven, are briefly discussed. It is shown that all the features as obtained from the present model are physically desirable and valid as far as the observed data set for the compact star $SAX~J1808.4-3658~(SS2)$ is concerned.

physics.gen-ph↗

arXiv2015

The Finslerian compact star model

We construct a toy model for compact stars based on the Finslerian structure of spacetime. By assuming a particular mass function, we find an exact solution of the Finsler-Einstein field equations with an anisotropic matter distribution. The solutions are revealed to be physically interesting and pertinent for the explanation of compact stars.

gr-qc↗

arXiv2015

Relativistic compact stars in $f(T)$ gravity admitting conformal motion

We provide a set of exact spherically symmetric solutions describing the interior of a relativistic star under f(T) modified gravity. To tackle the problem with lucidity we also assume the existence of a conformal Killing vector field within this f(T) gravity. We study several cases of interest to explore physically valid features of the solutions.

gr-qc↗

arXiv2015

Relativistic electromagnetic mass models in spherically symmetric spacetime

Under the static spherically symmetric Einstein-Maxwell spacetime of embedding class one we explore possibility of electromagnetic mass model where mass and other physical parameters have purely electromagnetic origin (Tiwari 1984, Gautreau 1985, Gron 1985). This work is in continuation of our earlier investigation (Maurya 2015a) where we developed an algorithm and found out three new solutions of electromagnetic mass models. In the present letter we consider different metric potentials $ν$ and $λ$ and analyzed them in a systematic way. It is observed that some of the previous solutions related to electromagnetic mass models are nothing but special cases of the presently obtained generalized solution set. We further verify the solution set and show that these are extremely applicable in the case of compact stars as well as for understanding structure of the electron.

gr-qc↗

arXiv2015

Anisotropic models for compact stars

In the present paper we obtain an anisotropic analogue of Durgapal-Fuloria (1985) perfect fluid solution. The methodology consists of contraction of anisotropic factor $Δ$ by the help of both metric potentials $e^ν$ and $e^λ$. Here we consider $e^λ$ same as Durgapal-Fuloria (1985) whereas $e^ν$ is that given by Lake (2003). The field equations are solved by the change of dependent variable method. The solutions set mathematically thus obtained are compared with the physical properties of some of the compact stars, strange star as well as white dwarf. It is observed that all the expected physical features are available related to stellar fluid distribution which clearly indicate validity of the model.

gr-qc↗

arXiv2015

Spherically symmetric electromagnetic mass models of embedding class one

In this article we consider the static spherically symmetric spacetime metric of embedding class one. Specifically three new electromagnetic mass models are derived where the solutions are entirely dependent on the electromagnetic field, such that the physical parameters, like density, pressure etc. do vanish for the vanishing charge. We have analyzed schematically all these three sets of solutions related to electromagnetic mass models by plotting graphs and shown that they can pass through all the physical tests performed by us. To validate these special type of solutions related to electromagnetic mass models a comparison has been done with that of compact stars and shown exclusively the feasibility of the models.

gr-qc↗

arXiv2015

A Dark Energy Model in Kaluza-Klein Cosmology

We study a dynamic $Λ$ model with varying gravitational constant $G$ under the Kaluza-Klein cosmology. Physical features and the limitations of the present model have been explored and discussed. Solutions are found mostly in accordance with the observed features of the accelerating universe. Interestingly, signature flipping of the deceleration parameter is noticed and the present age of the Universe is also attainable under certain stringent conditions. We find that the time variation of gravitational constant is not permitted without vintage $Λ$.

physics.gen-ph↗

arXiv2015

Wormhole inspired by non-commutative geometry

In the present work we search for a new wormhole solution inspired by noncommutative geometry with the additional condition of allowing conformal Killing vectors (CKV). A special aspect of noncommutative geometry is that it replaces point-like structures of gravitational sources with smeared objects under Gaussian distribution. However, the purpose of this paper is to obtain wormhole solutions with noncommutative geometry as a background where we consider a point-like structure of gravitational object without smearing effect. It is found through this investigation that wormhole solutions exist in this Lorentzian distribution with viable physical properties.

gr-qc↗

arXiv2015

Possibility of higher dimensional anisotropic compact star

We have provided here a new class of interior solutions for anisotropic stars admitting conformal motion in higher dimensional noncommutative spacetime. The Einstein fields equations are solved by choosing a particular density distribution function of Lorentzian type \cite{Nozari} under noncommutative geometry. Several cases with dimensions $4D$ and higher, e.g. $5D$, $6D$ and $11D$ have been discussed separately. An overall observation is that the model parameters, such as density, radial pressure, transverse pressure, anisotropy all are well behaved and represent a compact star with radius $4.17$ km. However, emphasis has been given on the acceptability of the model from physical point of view. As a consequence it is observed that higher dimensions, i.e. beyond $4D$ spacetime, exhibit several interesting yet bizarre features which are not at all untenable for a compact stellar model of strange quark type and thus dictates a possibility of its extra dimensional existence.

gr-qc↗

arXiv2015

Anisotropic stars with non-static conformal symmetry

We have proposed a model for relativistic compact star with anisotropy and analytically obtained exact spherically symmetric solutions describing the interior of the dense star admitting non-static conformal symmetry. Several features of the solutions including drawbacks of the model have been explored and discussed. For this purpose we have provided the energy conditions, TOV-equations and other physical requirements and thus thoroughly investigated stability, mass-radius relation and surface redshift of the model. It is observed that most of the features are well matched with the compact stars, like quark/strange stars.

gr-qc↗

arXiv2015

Fluid sphere: stability problem and dimensional constraint

We study different dimensional fluids inspired by noncommutative geometry which admit conformal Killing vectors. The solutions of the Einstein field equations examined specifically for five different set of spacetime. We calculate the active gravitational mass and impose stability conditions of the fluid sphere. The analysis thus carried out immediately indicates that at $4$-dimension only one can get a stable configuration for any spherically symmetric stellar system and any other dimensions, lower or higher, becomes untenable as far as the stability of a system is concerned.

gr-qc↗

arXiv2015

Possible existence of wormholes in the central regions of halos

An earlier study [Rahaman et al. (2014) & Kuhfittig (2014)] has demonstrated the possible existence of wormholes in the outer regions of the galactic halo, based on the Navarro-Frenk-White (NFW) density profile. This paper uses the Universal Rotation Curve (URC) dark matter model to obtain analogous results for the central parts of the halo. This result is an important compliment to the earlier result, thereby confirming the possible existence of wormholes in most of the spiral galaxies.

physics.gen-ph↗

arXiv2014

Possible features of galactic halo with electric field and observational constraints

Observed rotational curves of neutral hydrogen clouds strongly support the fact that galactic halo contains huge amount of nonluminous matter, the so called gravitational dark matter. The nature of dark matter is a point of debate among the researchers. Recent observations reported the presence of ions of O, S, C, Si etc in the galactic halo and intergalactic medium. This supports the possibility of existence of electric field in the galactic halo region. We therefore propose a model of galactic halo considering this electric field arising due to charged particles as one of the inputs for the background spacetime metric. Considering dark matter as an anisotropic fluid we obtain the expressions for energy density and pressure of dark matter there and consequently the equation of state of dark matter. Various other aspects of the solutions are also analyzed along with a critical comparison with and constraints of different observational evidences.

physics.gen-ph↗