arXiv subjects

F. Rahaman

Publications and source records attributed to F. Rahaman.

At least 19 recordsLinked to original sources

arXiv2022

Thin-shell wormhole under non-commutative geometry inspired Einstein-Gauss-Bonnet gravity

Einstein-Gauss-Bonnet gravity is a generalization of the general relativity to higher dimensions in which the first and second-order terms correspond to general relativity and Einstein-Gauss-Bonnet gravity respectively. We construct a new class of five-dimensional (5D) thin-shell wormholes by the `Cut-Paste' technique from black holes in Einstein-Gauss-Bonnet gravity inspired by non-commutative geometry starting with a static spherically symmetric, Gaussian mass distribution as a source and for this structural form of the thin shell wormhole we have explored several salient features of the solution, viz., pressure-density profile, equation of state, the nature of wormhole, total amount of exotic matter content at the shell. We have also analyzed the linearized stability of the constructed wormhole. From our study we can assert that our model is found to be plausible with reference to the other model of thin-shell wormhole available in literature.

gr-qc↗

arXiv2020

Plane symmetric cosmological models

In the present work, we execute the Lie symmetry analysis on the Einstein-Maxwell field equations in the plane symmetric spacetime. Under the background of the plane symmetric space-time we compute the Lie point symmetries, perform the similarity reductions and obtain exact solutions in connection to the evolutionary scenario of the universe. The special feature of the study is that it deals with the electromagnetic energy of the inhomogeneous universe through the non-vanishing component of electromagnetic field tensor $F_{12}$ and assumes that the free gravitational field is of Petrov type-II non-degenerate. We have found that the electromagnetic field tensor is positive and increasing function of time. To validate the solution set, we examine with detailed discussions several physical as well as geometrical features of a specific sub-case of the model.

physics.gen-ph↗

arXiv2019

Relativistic strange stars in Tolman-Kuchowicz spacetime

In this article we propose a relativistic model of a static spherically symmetric anisotropic strange star with the help of Tolman-Kuchowicz (TK) metric potentials [Tolman, Phys. Rev. {\bf55}, 364 (1939) and Kuchowicz, Acta Phys. Pol. {\bf33}, 541 (1968)]. The form of the potentials are $λ(r)=\ln(1+ar^2+br^4)$ and $ν(r)=Br^2+2\ln C$ where $a$, $b$, $B$ and $C$ are constants which we have to evaluate using boundary conditions. We also consider the simplest form of the phenomenological MIT bag equation of state (EOS) to represent the strange quark matter (SQM) distribution inside the stellar system. Here, the radial pressure $p_r$ relates with the density profile $ρ$ as follows, $p_r(r)=\frac{1}{3}[ρ(r)-4B_g]$, where $B_g$ is the Bag constant. To check the physical acceptability and stability of the stellar system based on the obtained solutions, we have performed various physical tests. It is shown that the model satisfies all the stability criteria, including nonsingular nature of the density and pressure, implies stable nature. Here, the Bag constant for different strange star candidates are found to be $(68-70)$~MeV/{fm}$^3$ which satisfies all the acceptability criteria and remains in the experimental range.

gr-qc↗

arXiv2019

On the energy of a non-singular black hole solution satisfying the weak energy condition

The energy-momentum localization for a new four-dimensional and spherically symmetric, charged black hole solution that through a coupling of general relativity with non-linear electrodynamics is everywhere non-singular while it satisfies the weak energy condition is investigated. The Einstein and M\{o} ller energy-momentum complexes have been employed in order to calculate the energy distribution and the momenta for the aforesaid solution. It is found that the energy distribution depends explicitly on the mass and the charge of the black hole, on two parameters arising from the space-time geometry considered, and on the radial coordinate. Further, in both prescriptions all the momenta vanish.In addition, a comparison of the results obtained by the two energy-momentum complexes is made, whereby some limiting and particular cases are pointed out.

gr-qc↗

arXiv2018

Strange stars in Krori-Barua space-time under f(R; T) gravity

In the present work, we study about highly dense compact stars which are made of quarks, specially strange quarks, adopting the Krori-Barua (KB)~\cite{Krori1975} metric in the framework of $f(R,T)$ gravity. The equation of state (EOS) of a strange star can be represented by the MIT bag model as $p_r(r)=\frac{1}{3}[ρ(r)-4B_g]$ where $B_g$ is the bag constant, arises due to the quark pressure. Main motive behind our study is to find out singularity free and physically acceptable solutions for different features of strange stars. Here we also investigate the effect of alternative gravity in the formation of strange stars. We find that our model is consistent with various energy conditions and also satisfies Herrera's cracking condition, TOV equation, static stability criteria of Harrison-Zel$'$dovich-Novikov etc. The value of the adiabatic indices as well as the EOS parameters re-establish the acceptability of our model. Here in detail we have studied specifically three different strange star candidates, viz. $PSRJ~1614~2230, Vela~X-1$ and $Cen~X-3$. As a whole, present model fulfils all the criteria for stability. Another fascinating point we have discussed is the value of the bag constant which lies in the range $(40-45)$~MeV/fm$^{3}$. This is quite smaller than the predicted range, i.e., $(55-75)$~MeV/fm$^{3}$ ~\cite{Farhi1984,Alcock1986}. The presence of the constant ($χ$), arises due to the coupling between matter and geometry, is responsible behind this reduction in $B_g$ value. For $χ=0$, we get the higher value for $B_g$ as the above mentioned predicted range.

gr-qc↗

arXiv2017

Compact star in pseudo-spheroidal spacetime

We investigate perfect fluid stars in $(2+1)$ dimension in pseudo spheroidal spacetime with the help of Vaidya-Tikekar metric where the physical $3$-space ($t=$ constant) is described by pseudo-spheroidal geometry. Here the spheroidicity parameter $a$, plays an important role for determining the properties of a compact star. In the present work a class of interior solutions corresponding to the Ba$\tilde{n}$ados-Teitelboim-Zanelli $(BTZ)$ (Bañados et al., Phys. Rev. Lett. 69:1849, 1992) exterior metric has been provided which describes a static circularly symmetric star with negative cosmological constant in equilibrium. It is shown that asymptotically anti-de Sitter $(2+1)$ dimensional spacetime described by BTZ admits a compact star solution with reasonable physical features.

physics.gen-ph↗

arXiv2016

Interior Solutions of Fluid Sphere in f(R,T) Gravity Admitting Conformal Killing Vectors

We discuss the interior solutions of fluid Sphere in f(R,T) gravity admitting conformal killing vectors, where R is Ricci scalar and T is trace of energy momentum tensor. The solutions corresponding to isotropic and anisotropic configurations have been investigated explicitly. Further, the anisotropic case has been dealt by the utilization of linear equation of state. The results for both cases have been interpreted graphically. The equation of state parameter, integration constants and other parameters of the theory have been chosen to find the central density equal to standard value of central density of the compact objects. The energy conditions as well as stability of the solutions have been investigated in the background of f(R,T) gravity.

gr-qc↗

arXiv2016

$C$-field cosmological models: revisited

We investigate plane symmetric space-time filled with perfect fluid in the $C$-field cosmology of Hoyle and Narlikar. A new class of exact solutions have been obtained by considering the creation field $C$ as a function of time only. To get the deterministic solution, it has been assumed that the rate of creation of matter-energy density is proportional to the strength of the existing $C$-field energy density. Several physical aspects and geometrical properties of the models are discussed in detail, especially it is shown that some of our solutions of $C$-field cosmology are free from singularity in contrast to the Big Bang cosmology. A comparative study has been carried out between two models, one singular and the other nonsingular, by contrasting the behaviour of the physical parameters and noted that the model in a unique way represents both the features of the accelerating as well as decelerating Universe depending on the parameters and thus seems provides glimpses of the oscillating or cyclic model of the Universe without invoking any other agent or theory in allowing cyclicity.

physics.gen-ph↗

arXiv2014

Bianchi type-I, type-III and Kantowski-Sachs solutions in f(T) gravity

In the context of modified tele-parallel theory of gravity, we undertake cosmological anisotropic models and search for their solutions. Within a suitable choice of non-diagonal tetrads, the decoupled equations of motion are obtained for Bianchi-I, Bianchi-III and Kantowski-Sachs models, from which we obtain the correspondent solutions. By the way, energy density and pressures are also obtained, showing, as an important result, that our universe may live a quintessence like universe even still anisotropic models are considered.

gr-qc↗

arXiv2014

About influence of gravity on heat conductivity process of the Planets

In the present study it is shown that the interaction of a quasi-static gravitational wave through density fluctuations gives rise to a heat conductivity coefficient and hence temperature. This fact is a very important characteristics to establish a heat equilibrium process of such massive body as the Earth and other Planets. To carry out this exercise general mechanism has been provided, which makes a bridge between classical physics and quantum theory, and specific dependence of heat conductivity coefficient in wide region is also calculated.

physics.gen-ph↗

arXiv2014

Energy distribution of a regular black hole solution in Einstein-nonlinear electrodynamics

In this work a study about the energy-momentum of a new four-dimensional spherically symmetric, static and charged, regular black hole solution developed in the context of general relativity coupled to nonlinear electrodynamics is presented. Asymptotically, this new black hole solution behaves as the Reissner-Nordström solution only for the particular value μ=4, where μ is a positive integer parameter appearing in the mass function of the solution. The calculations are performed by use of the Einstein, Landau-Lifshitz, Weinberg and Møller energy-momentum complexes. In all the aforesaid prescriptions, the expressions for the energy of the gravitating system considered depend on the mass M of the black hole, its charge q, a positive integer α and the radial coordinate r. In all these pseudotensorial prescriptions the momenta are found to vanish, while the Landau-Lifshitz and Weinberg prescriptions give the same result for the energy distribution. In addition, the limiting behavior of the energy for the cases r tends toward infinity, r=0 and q=0 is studied. The special case μ=4 and α=3 is also examined. We conclude that the Einstein and Møller energy-momentum complexes can be considered as the most reliable tools for the study of the energy-momentum localization of a gravitating system.

gr-qc↗

arXiv2013

On Topological Defects and Cosmological Constant

Einstein introduced Cosmological Constant in his field equations in an ad hoc manner. Cosmological constant plays the role of vacuum energy of the universe which is responsible for the accelerating expansion of the universe. To give theoretical support it remains an elusive goal to modern physicists. We provide a prescription to obtain cosmological constant from the phase transitions of the early universe when topological defects, namely monopole might have existed.

physics.gen-ph↗

arXiv2012

Anisotropic Universe Models in f(T) Gravity

We investigate the cosmological reconstruction in anisotropic universe for both homogeneous and inhomogeneous content of the universe. Special attention is attached to three interesting cases: Bianchi type-I, Bianchi type-III and Kantowski-Sachs models. The de Sitter, power-law and general exponential solutions are assumed for the scale factor in each spatial direction and the corresponding cosmological models are reconstructed. Moreover, for the general exponential solutions, from which the de Sitter and power-law solutions may be obtained, we obtain models which reproduce the early universe, assumed as the inflation, and the late time accelerated expanding universe. The models obtained for the late time universe are consistent with a known result in literature where a power-law type correction in T is added to a power-law type of f(T) for guaranteeing the avoidance of the Big Rip and the Big Freeze.

gr-qc↗

arXiv2012

Galactic rotation curves inspired by a noncommutative-geometry background

This paper discusses the observed at rotation curves of galaxies in the context of noncommutative geometry. The energy density of such a geometry is diffused throughout a region due to the uncertainty encoded in the coordinate commutator. This intrinsic property appears to be sufficient for producing stable circular orbits, as well as attractive gravity, without the need for dark matter.

gr-qc↗

arXiv2012

Energy Distribution for Non-commutative Radiating Schwarzschild Black Holes

The aim of this article is the calculation of the energy-momentum for a non-commutative radiating Schwarzschild black hole in order to obtain the expressions for energy. We make the calculations with the Einstein and M\oller prescriptions. We show that the expressions for energy in both the prescriptions depend on the mass $M$, $θ$ parameter and radial coordinate. We make some comparisons between the results. Our results show that the Einstein prescription is a more powerful concept than the M\oller prescription.

gr-qc↗

arXiv2011

Thin-shell wormholes from black holes with dilaton and monopole fields

We provide a new type of thin-shell wormhole from the black holes with dilaton and monopole fields. The dilaton and monopole that built the black holes may supply fuel to construct the wormholes. Several characteristics of this thin-shell wormhole have been discussed. Finally, we discuss the stability of the thin-shell wormholes with a "phantom-like" equation of state for the exotic matter at the throat.

gr-qc↗

arXiv2011

On the energy of Hořava-Lifshitz black holes

In this paper we calculate the energy distribution of the Mu-in Park, Kehagias-Sfetsos (KS) and Lü, Mei and Pope (LMP) black holes in the Hořava-Lifshitz theory of gravity. These black hole solutions correspond to the standard Einstein-Hilbert action in the infrared limit. For our calculations we use the Einstein and Møller prescriptions. Various limiting and particular cases are also discussed.

gr-qc↗

arXiv2011

Modeling galactic halos with predominantly quintessential matter

This paper discusses a new model for galactic dark matter by combining an anisotropic pressure field corresponding to normal matter and a quintessence dark energy field having a characteristic parameter $ω_q$ such that $-1<ω_q< -\frac{1}{3}$. Stable stellar orbits together with an attractive gravity exist only if $ω_q$ is extremely close to $-\frac{1}{3}$, a result consistent with the special case studied by Guzman et al. (2003). Less exceptional forms of quintessence dark energy do not yield the desired stable orbits and are therefore unsuitable for modeling dark matter.

gr-qc↗