arXiv subjects

Debabrata Deb

Publications and source records attributed to Debabrata Deb.

At least 37 records · Page 2Linked to original sources

arXiv2019

Study on charged strange stars in $f\left(R,\mathcal{T}\right)$ gravity

We investigate effects of the modified $f(R, \mathcal{T})$ gravity on the charged strange quark stars with the standard choice of $f(R, \mathcal{T})=R+2χ\mathcal{T}$. Those types of stars are supposed to be made of strange quark matter (SQM) whose distribution is governed by the phenomenological MIT bag EOS as $p=\frac{1}{3}(ρ-4B)$, where $B$ is the bag constant, while the form of charge distribution is chosen to be $q\left(r\right)=Q\left(r/R\right)^3=αr^3$ with $α$ as a constant. We derive the values of the unknown parameters by matching the interior spacetime to the exterior Reissner-Nordstr{ö}m metric followed by the appropriate choice of the values of the parameters $χ$ and $α$. Our study reveals that besides SQM, a new kind of matter distribution originates due to the interaction between the matter and the extra geometric term, while the modification of the Tolman-Oppenheimer-Volkoff (TOV) equation invokes the presence of a new force $F_c$. The accumulation of the electric charge distribution reaches its maximum at the surface, and the predicted values of the corresponding electric charge and electric field are of the order of $10^{19-20}$ C and $10^{21-22}$ V/cm, respectively. To examine the physical validity of our solutions, we perform several tests and find that the proposed $f(R, \mathcal{T})$ model survives all these critical tests. Therefore, our model can describe the non-singular charged strange stars and justify the supermassive compact stellar objects having their masses beyond the maximum mass limit for the compact stars in the standard scenario. Our model also supports the existence of several exotic astrophysical objects like super-Chandrasekhar white dwarfs, massive pulsars, and even magnetars, which remain unexplained in the framework of General Relativity (GR).

gr-qc↗

arXiv2019

Study on anisotropic strange stars in $f(R,T)$ gravity: An embedding approach under simplest linear functional of matter-geometry coupling

The present work is focused on the investigation of the existence of compact structures describing anisotropic matter distributions within the framework of modified gravity theories, specifically f(R,$\mathcal{T}$) gravity theory. Additionally, we have taken f(R,$\mathcal{T}$) as a linear function of the Ricci scalar $R$ and the trace of the energy-momentum tensor $\mathcal{T}$ as $f(R,\mathcal{T})$=$R+2χ\mathcal{T}$,where $χ$ is a dimensionless coupling parameter, and the Lagrangian matter $\mathcal{L}_m=-\frac{1}{3}\left(2p_{t}+p_{r}\right)$, to describe the complete set of field equations for the anisotropic matter distribution. We follow the embedding class one procedure using Eisland condition to obtain a full space-time description inside the stellar configuration. Once the space-time geometry is specified we determine the complete solution of the modified Einstein equations by using the MIT bag model equation of state $p_{r}=\frac{1}{3}\left(ρ-4B\right)$ that describes the strange quark matter (SQM) distribution inside the stellar system, where $B$ denotes a bag constant. The physical validity of our anisotropic solution is confirmed by executing several physical tests. It is worth mentioning that with the help of the observed mass values for the various strange star candidates we have predicted the exact radii by taking different values for $χ$ and $B$. These predicted radii show monotonic decreasing nature as the parameter $χ$ is moved from $-0.8$ to $0.8$ progressively. In this case, our anisotropic stellar system becomes more massive and transforms into more dense compact stars.

gr-qc↗

arXiv2019

Noncommutative black hole in the Finslerian spacetime

We study the behavior of the noncommutative radiating Schwarzschild black hole in the Finslerian spacetime. The investigation shows that black hole possesses either (i) two horizons, or (ii) a single horizon, or (iii) no horizon corresponding to a minimal mass. We obtain that the minimal mass significantly changes with the Finslerian parameter, keeping minimal horizon remain unchanged. It turns out that under Finslerian spacetime, the maximum temperature before cooling down to absolute zero varies with Finslerian parameter. We then study the stability of the black hole by analyzing the specific heat and free energy. The energy conditions, their violation limit also scrutinized. Our findings suggest a stable black hole remnant, whose mass and size are uniquely determined in terms of the Finslerian parameter $\overline{Ric}$ and noncommutative parameter $θ$. The physical relevance of these results are discussed in a brief.

physics.gen-ph↗

arXiv2019

Exploring physical features of anisotropic strange stars beyond standard maximum mass limit in $f\left(R,\mathcal{T}\right)$ gravity

We study a specific model of anisotropic strange stars in the modified $f\left(R,\mathcal{T}\right)$-type gravity by deriving solutions to the modified Einstein field equations representing a spherically symmetric anisotropic stellar object. We take a standard assumption that $f(R,\mathcal{T})=R+2χ\mathcal{T}$, where $R$ is Ricci scalar, $\mathcal{T}$ is the trace of the energy-momentum tensor of matter, and $χ$ is a coupling constant. To obtain our solution to the modified Einstein equations, we successfully apply the `embedding class 1' techniques. We also consider the case when the strange quark matter (SQM) distribution is governed by the simplified MIT bag model equation of state given by $p_r=\frac{1}{3}\left(ρ-4B\right)$, where $B$ is bag constant. We calculate the radius of the strange star candidates by directly solving the modified TOV equation with the observed values of the mass and some parametric values of $B$ and $χ$. The physical acceptability of our solutions is verified by performing several physical tests. Interestingly, besides the SQM, another type of matter distribution originates due to the effect of coupling between the matter and curvature terms in the $f\left(R,\mathcal{T}\right)$ gravity theory. Our study shows that with decreasing the value of $χ$, the stellar systems under investigations become gradually massive and larger in size, turning them into less dense compact objects. It also reveals that for $χ<0$ the $f\left(R,\mathcal{T}\right)$ gravity emerges as a suitable theory for explaining the observed massive stellar objects like massive pulsars, super-Chandrasekhar stars and magnetars, etc., which remain obscure in the standard framework of General Relativity (GR).

gr-qc↗

arXiv2019

Anisotropic strange star in Finsler geometry

In the present paper, we report on a study of the anisotropic strange stars under Finsler geometry. Keeping in mind that Finsler spacetime is not merely a generalization of Riemannian geometry rather the main idea is the projectivized tangent bundle of the manifold $\mathpzc{M}$, we have developed the respective field equations. Thereafter, we consider the strange quark distribution inside the stellar system followed by the MIT bag model equation of state (EOS). To find out the stability and also the physical acceptability of the stellar configuration, we perform in detail some basic physical tests of the proposed model. The results of the testing show that the system is consistent with the Tolman-Oppenheimer-Volkoff (TOV) equation, Herrera cracking concept, different energy conditions and adiabatic index. One important result that we observe is that the anisotropic stress reaches to the maximum at the surface of the stellar configuration. We calculate (i) the maximum mass as well as corresponding radius, (ii) the central density of the strange stars for finite values of bag constant $B_g$ and (iii) the fractional binding energy of the system. This study shows that Finsler geometry is especially suitable to explain massive stellar systems.

gr-qc↗

arXiv2019

Charged anisotropic strange stars in Finslerian geometry

We investigate a simplified model for the strange stars in the framework of Finslerian spacetime geometry, composed of charged fluid. It is considered that the fluid consisting of three flavor quarks including a small amount of non-interacting electrons to maintain the chemical equilibrium and assumed that the fluid is compressible by nature. To obtain the simplified form of charged strange star we considered constant flag curvature. Based on geometry, we have developed the field equations within the localized charge distribution. We considered that the strange quarks distributed within the stellar system are compiled with the MIT bag model type of equation of state (EOS) and the charge distribution within the system follows a power law. We represent the exterior spacetime by the Finslerian Ressiner-Nordstr{ö}m space-time. The maximum anisotropic stress is obtained at the surface of the system. Whether the system is in equilibrium or not, has been examined with respect to the Tolman-Oppenheimer-Volkoff (TOV) equation, Herrera cracking concept, different energy conditions and adiabatic index. We obtain that the total charge is of the order of 10$^{20}$ C and the corresponding electric field is of around 10$^{22}$ V/m. The central density and central pressure vary inversely with the charge. Varying the free parameter (charge constant) of the model, we find the generalized mass-radius variation of strange stars and determine the maximum limited mass with the corresponding radius. Furthermore, we also considered the variation of mass and radius against central density respectively.

gr-qc↗

arXiv2018

Anisotropic compact stars in f(T) gravity under Karmarkar condition

In this study, we present a generalized spherically symmetric, anisotropic and static compact stellar model in $f(T)$ gravity, where $T$ represents the torsion scalar. By employing the Karmarkar condition we have obtained embedding class 1 metric from the general spherically metric of class 2 and the solutions of the Einstein field equations (EFE) has been presented with the choice of suitable parametric values of $n$ under a simplified linear form of $f(T)$ gravity reads as $f(T)=A+BT$, where $A$ and $B$ are two constants. By matching the interior spacetime metric with the exterior Schwarzschild metric at the surface and considering the values of mass and radius of the compact stars we obtain the values of the unknown constants. We have presented further a detailed analysis of the physical acceptability and examined the stability of the stellar configuration by studying the energy conditions, generalized Tolman-Oppenheimer-Volkov (TOV) equation, Herrera cracking concept, adiabatic index, etc. In the investigation, we predict numerical values of the central density, surface density, central pressure, etc., in a tabular form taking different values of $n$ specifically for $LMC~X-4$, $Cen~X-3$ and $SMC~X-1$ as the representative of compact star candidates.

gr-qc↗

arXiv2018

A New Model for Strange Stars

In the present work, we attempt to find a new class of solutions for the spherically symmetric perfect fluid sphere by employing the Homotopy Perturbation Method (HPM), a new tool via which the mass polynomial function facilitates to tackle the Einstein field equations. A set of interior solutions found on the basis of the simplest MIT bag model equation of state (EOS) in the form $p=\frac{1}{3}(ρ-4B)$ where $B$ is the bag constant. The proposed interior metric for the stellar system is consistent with the exterior Schwarzschild spacetime on the boundary. In addition, we also conduct a detailed study on different tests, viz. the energy conditions, TOV equation, adiabatic index, Buchdahl limit, etc., to verify the physical validity of the proposed model. The numerical value of the used parameters is predicted for different strange star candidates, for different chosen values of the bag constant. In a nutshell, by exploiting HPM technique first time ever in the field of relativistic astrophysics, we have predicted in the present literature a singularity-free and stable stellar model which is suitable to describe ultra-dense objects, like strange (quark) stars.

gr-qc↗

arXiv2018

Anisotropic strange stars in Tolman-Kuchowicz spacetime

We attempt to study a singularity-free model for the spherically symmetric anisotropic strange stars under Einstein's general theory of relativity by exploiting the Tolman-Kuchowicz metric. Further, we have assumed that the cosmological constant $Λ$ is a scalar variable dependent on the spatial coordinate $r$. To describe the strange star candidates we have considered that they are made of strange quark matter (SQM) distribution, which is assumed to be governed by the MIT bag equation of state. To obtain unknown constants of the stellar system we match the interior Tolman-Kuchowicz metric to the exterior modified Schwarzschild metric with the cosmological constant, at the surface of the system. Following Deb et al. we have predicted the exact values of the radii for different strange star candidates based on the observed values of the masses of the stellar objects and the chosen parametric values of the $Λ$ as well as the bag constant $\mathcal{B}$. The set of solutions satisfies all the physical requirements to represent strange stars. Interestingly, our study reveals that as the values of the $Λ$ and $\mathcal{B}$ increase the anisotropic system becomes gradually smaller in size turning the whole system into a more compact ultra-dense stellar object.

gr-qc↗

arXiv2018

Anisotropic strange stars with Tolman V potential

In this paper we present a strange stellar model using Tolman $V$ type metric potential employing simplest form of the MIT bag equation of state (EOS) for the quark matter. We consider that the stellar system is spherically symmetric, compact and made of an anisotropic fluid. Choosing different values of $n$ we obtain exact solutions of the Einstein field equations and finally conclude that for a specific value of the parameter $n=1/2$ we find physically acceptable features of the stellar object. Further we conduct different physical tests, viz., the energy condition, generalized TOV equation, Herrera's cracking concept, etc., to confirm physical validity of the presented model. Matching conditions provide expressions for different constants whereas maximization of the anisotropy parameter provides bag constant. By using the observed data of several compact stars we derive exact values of some of the physical parameters and exhibit their features in a tabular form. It is to note that our predicted value of the bag constant satisfies the report of CERN-SPS and RHIC.

gr-qc↗

arXiv2018

Strange stars in $f(R,\mathcal{T})$ gravity

In this article we try to present spherically symmetric isotropic strange star model under the framework of $f(R,\mathcal{T})$ theory of gravity. To this end, we consider that the Lagrangian density is an arbitrary linear function of the Ricci scalar $R$ and the trace of the energy momentum tensor~$\mathcal{T}$ given as $f\left(R,\mathcal{T}\right)=R+2χT$. We also assume that the quark matter distribution is governed by the simplest form of the MIT bag model equation of state (EOS) as $p=\frac{1}{3}\left(ρ-4B\right)$, where $B$ is the bag constant. We have obtained an exact solution of the modified form of the the Tolman-Oppenheimer-Volkoff (TOV) equation in the framework of $f(R,\mathcal{T})$ gravity theory and studied the dependence of different physical properties, viz., total mass, radius, energy density and pressure on the chosen values of $χ$. Further, to examine physical acceptability of the proposed stellar model in detail, we conducted different tests, viz. energy conditions, modified TOV equation, mass-radius relation, causality condition etc. We have precisely explained the effects arising due to the coupling of the matter and geometry on the compact stellar system. For a chosen value of the Bag constant we have predicted numerical values of different physical parameters in tabular format for the different strange stars. It is found that as the factor $χ$ increases the strange stars shrink gradually and become less massive to turn into a more compact stellar system. The maximum mass point is well within the observational limits and hence our proposed model is suitable to explain the ultra dense compact stars. For $χ=0$ we retrieve as usual the standard results of general relativity (GR).

gr-qc↗

arXiv2018

Anisotropic strange stars under simplest minimal matter-geometry coupling in the $f(R,\mathcal{T})$ gravity

We study strange stars in the framework of $f\left(R,\mathcal{T}\right)$ theory of gravity where the strange quark matter distribution inside the stellar system is governed by the phenomenological MIT Bag model equation of state (EOS). Further, for a specific value of $B$ and observed values of mass of the strange star candidates we obtain the exact solution of the modified Tolman-Oppenheimer-Volkoff (TOV) equation in the framework of $f\left(R,\mathcal{T}\right)$ gravity and have studied in detail the dependence of the different physical parameters due to the chosen different values of $χ$. To check the physical acceptability and stability of the stellar system based on the obtained solutions we have performed different physical tests, viz., the energy conditions, Herrera cracking concept, adiabatic index etc. In this work, we also have explained the effects, those are arising due to the interaction between the matter and the curvature terms in $f\left(R,\mathcal{T}\right)$ gravity, on the anisotropic compact stellar system. It is interesting to note that as the values of $χ$ increase the strange stars become more massive and their radius increase gradually so that eventually they gradually turn into less dense compact objects. The present study reveals that the modified $f\left(R,\mathcal{T}\right)$ gravity is a suitable theory to explain massive stellar systems like recent magnetars, massive pulsars and super-Chandrasekhar stars, which can not be explained in the framework of GR. However, for $χ=0$ the standard results of Einsteinian gravity are retrieved.

physics.gen-ph↗

arXiv2018

Compact stars: a generalized model

This paper discusses a generalized model for compact stars, assumed to be anisotropic in nature due to the spherical symmetry and high density. After embedding the four-dimensional spacetime in a five-dimensional flat spacetime, which may be treated as an alternative to Karmarkar's condition of embedding class 1 spacetime, the Einstein field equations were solved by employing a class of physically acceptable metric functions proposed by Lake \cite{Lake2003}. The physical properties determined include the anisotropic factor showing that the anisotropy is zero at the center and maximal at the surface. Other boundary conditions yielded the values of various parameters needed for rendering the numerous plots and also led to the EOS parameters. It was further determined that the usual energy conditions are satisfied and that the compact structures are stable, based on several criteria, starting with the TOV equation. The calculation of the effective gravitational mass shows that the models satisfy the Buchdahl condition. Finally, the values of the numerous constants and physical parameters were determined specifically for the strange star LMCX-4. It is shown that the present generalized model can justify most off the compact stars including white dwarfs and ultra dense compact stars for a suitable tuning of the parametric values of $n$.

physics.gen-ph↗

arXiv2018

Anisotropic strange stars in the Einstein-Maxwell spacetime

We present here a detailed analysis on the effects of charge on the anisotropic strange star candidates by considering a spherically symmetric interior spacetime metric. To obtain exact solution of the Einstein-Maxwell field equations we have considered the anisotropic strange quark matter (SQM) distribution governed by the simplified MIT bag equation of state (EOS), $p=\frac{1}{3}\left( ρ-4\,B \right)$, where $B$ is the bag constant and the distribution of the electrical charge is given as $q(r)=Q\left({r}/{R}\right)^3=α{r^3}$, where $α$ is a constant. To this end, to calculate different constants we have described the exterior spacetime by the Reissner-Nordstr{ö}m metric. By using the values of the observed mass for the different strange star candidates we have maximized anisotropic stress at the surface to predict the exact values of the radius for the different values of $α$ and a specific value of the bag constant. Further, we perform different tests to study the physical validity and the stability of the proposed stellar model. We found accumulation of the electric charge distribution is maximum at the surface having electric charge of the order ${{10}^{20}}~C$ and electric field of the order ${10}^{21-22}~V/cm$. To study the different physical parameters and the effects of charge on the anisotropic stellar system we have presented our analysis graphically and in the tabular format by considering $LMC~X-4$ as the representative of the strange star candidates.

gr-qc↗

arXiv2017

Exact Radiation Model For Perfect Fluid Under Maximum Entropy Principle

We find the Euler-Lagrangian equation by maximising the total entropy. Hence we obtain an expression for mass of the spherically symmetric system by solving the Euler-Lagrangian equation where the Homotopy Perturbation Method has been employed. With the help of this expression and the Einstein field equations we obtain an interior solution set. Thereafter, we explain different aspects of the solution describing the system in connection to the mass, density, pressures, energy, stability, mass-radius ratio, compactness factor and surface redshift. This analysis shows that all the physical properties, in connection to brown dwarf stars, are valid with the observed features.

physics.gen-ph↗

arXiv2017

Relativistic model for anisotropic strange stars

In this article, we attempt to find a singularity free solution of Einstein's field equations for compact stellar objects, precisely strange (quark) stars, considering Schwarzschild metric as the exterior spacetime. To this end, we consider that the stellar object is spherically symmetric, static and anisotropic in nature and follows the density profile given by Mak and Harko (2002), which satisfies all the physical conditions. To investigate different properties of the ultra-dense strange stars we have employed the MIT bag model for the quark matter. Our investigation displays an interesting feature that the anisotropy of compact stars increases with the radial coordinate and attains its maximum value at the surface which seems an inherent property for the singularity free anisotropic compact stellar objects. In this connection we also perform several tests for physical features of the proposed model and show that these are reasonably acceptable within certain range. Further, we find that the model is consistent with the energy conditions and the compact stellar structure is stable with the validity of the TOV equation and Herrera cracking concept. For the masses bellow the maximum mass point in mass vs radius curve the typical behavior achieved within the framework of general relativity. We have calculated the maximum mass and radius of the strange stars for the three finite values of bag constant $B_g$.

gr-qc↗

arXiv2017

On the features of Matese-Whitman mass function

In the present paper we exhaustively examine the physical status of the socalled Matese-Whitman mass function [J.J. Matese and P.G. Whitman, Phys. Rev. D, 22, 1270 (1980)]. As a first step, we construct the relevant Einstein field equations with an anisotropic matter distribution under the approach of Conformal killing Vector. In the intermideate step we find a set of exact solutions by using the Matese-Whitman mass function. Eventually we conduct several physical tests to explore features of the applied mass function in connection to the specific compact stars. It can be observed that all the features of the model based on the Matese-Whitman mass function are of physical interests.

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↗