arXiv subjects

Farook Rahaman

Publications and source records attributed to Farook Rahaman.

At least 145 records · Page 8Linked to original sources

arXiv2015

Search of wormholes in different dimensional non-commutative inspired space-time with lorentzian distribution

In this paper we are searching whether the wormhole solutions exists in different dimensional non- commutative inspired spacetimes. It is well known that the noncommutativity of the space is an outcome of string theory and it replaced the usual point like object by a smeared object. Here we have chosen Lorentzian distribution as the density function in the noncommutative inspired space- time. We have observed that the wormhole solutions exist only in four and five dimension, however, higher than fine dimension no wormhole exists. For five dimensional spacetime, we get a wormhole for a restricted region. In usual four dimensional spacetime, we get a stable wormhole which is asymptotically flat.

physics.gen-ph↗

arXiv2015

The Dark Energy Star and Stability analysis

We have proposed a new model of dark energy star consisting of five zones namely, solid core of constant energy density, the thin shell between core and interior, an inhomogeneous interior region with anisotropic pressures, thin shell and the exterior vacuum region. We have discussed various physical properties. The model satisfies all the physical requirements. The stability condition under small linear perturbation has also been discussed.

physics.gen-ph↗

arXiv2015

Some Invariant String Cosmological Models in Cylindrically Symmetric Space-time

In this paper we derive some new invariant solutions of Einstein-Maxwell's field equations for string fluid as source of matter in cylindrically symmetric space-time with Variable Magnetic Permeability. We also discuss the physical and eometrical properties of the models derived in the paper. The solutions, at least one of them, are interesting physically as they can explain the accelerating as well as singularity free Universe.

gr-qc↗

arXiv2015

Emergence and Expansion of Cosmic Space in BIonic system

Recently, Padmanabhan [arXiv:1206.4916] argued that the expansion rate of the universe can be thought of as the emergence of space as cosmic time progresses and is related to the difference between the surface degrees of freedom on the holographic horizon and the bulk degrees of freedom inside. The main question arises as to what is origin of emergence of space in 4D universe? We answer to this question in BIonic system. The BIon is a configuration in flat space of a D-brane and a parallel anti-D-brane connected by a thin shell wormhole with F-string charge. We propose a new model that allows all degrees of freedom inside and outside the universe are controlled by the evolutions of BIon in extra dimension and tend to degrees of freedom of black F-string in string theory or black M2-brane in M theory.

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↗

arXiv2014

Exact solutions in (2 + 1)-dimensional anti-de Sitter space-time admitting a linear or non-linear equation of state

Gravitational analyzes in lower dimensions has become a field of active research interest ever since Banados, Teitelboim and Zanelli (BTZ) (Phys. Rev. Lett. 69, 1849, 1992) proved the existence of a black hole solution in (2 + 1) dimensions. The BTZ metric has inspired many investigators to develop and analyze circularly symmetric stellar models which can be matched to the exterior BTZ metric. We have obtained two new classes of solutions for a (2 + 1)-dimensional anisotropic star in anti-de Sitter background space-time which have been obtained by assuming that the equation of state (EOS) describing the material composition of the star could either be linear or non-linear in nature. By matching the interior solution to the BTZ exterior metric with zero spin, we have demonstrated that the solutions provided here are regular and well-behaved at the stellar interior.

gr-qc↗

arXiv2014

A new deterministic model of strange stars

The observed evidence for the existence of strange stars and the concomitant observed masses and radii are used to derive an interpolation formula for the mass as a function of the radial coordinate. The resulting general mass function becomes an effective model for a strange star. The analysis is based on the MIT bag model and yields the energy density, as well as the radial and transverse pressures. Using the interpolation function for the mass, it is shown that a mass-radius relation due to Buchdahl is satisfied in our model. We find the surface redshift ($Z$) corresponding to the compactness of the stars. Finally, from our results, we predict some characteristics of a strange star of radius 9.9 km.

gr-qc↗

arXiv2014

A new relativistic model of hybrid star with interactive quark matter and dense baryonic matter

We propose a relativistic model of hybrid star admitting conformal symmetry considering quark matter and baryonic matter as two different fluids. We define interaction equations between the normal baryonic matter and the quark matter and study the physical situations for repulsive, attractive and zero interaction between the constituent matters. From the interaction equations we find out the value of the equation of state (EOS) parameter for normal baryonic matter which is found to be consistent with the value obtained from the Walecka model for nucleonic matter at high density. The measured value of the Bag constant is used to explore the space time geometry inside the star. The theoretical mass-radius values are compared with the available observational data of the compact objects. From the nature of the match with the observational data, we predict the nature of interaction that must be present inside the hybrid stars

gr-qc↗

arXiv2014

Exact solution of a (2 + 1) dimensional anisotropic star in Finch and Skea spacetime

We provide a new class of interior solution of a (2 + 1) dimensional anisotropic star in Finch and Skea spacetime corresponding to the BTZ black hole. We have developed the model by considering the MIT bag model EOS and a particular ansatz for the metric function $ g_{rr}$ proposed by Finch and Skea \cite{FS}. Our model is free from central singularity and satisfied all the physical requirements for the acceptability of the model.

physics.gen-ph↗

arXiv2014

Charged star in (2+1)-dimensional gravity

We obtain a new class of exact solutions for the Einstein-Maxwell system in static spherically symmetric charged star in (2+1)-dimensional gravity. In order to obtain the analytical solutions we treat the matter distribution anisotropic in nature admitting linear or nonlinear equation of state and the electric field intensity was specified. By choosing a suitable choice of mass function m(r), it is possible to integrate the system in closed form. All the solution, which are obtained in both linear and nonlinear cases are regular at the center and well behaved in the stellar interior.

gr-qc↗

arXiv2014

Analytical model of strange star in the low-mass X-ray binary 4U 1820-30

In this article, we have proposed a model for a realistic strange star under Tolman VII metric\citep{Tolman1939}. Here the field equations are reduced to a system of three algebraic equations for anisotropic pressure. Mass, central density and surface density of strange star in the low-mass X-ray binary 4U 1820-30 has been matched with the observational data according to our model. Strange materials clearly satisfies the stability condition (i.e. sound velocities < 1) and TOV-equation. Here also surface red shift of the star has been found to be within reasonable limit.

gr-qc↗

arXiv2014

The higher dimensional gravastars

A new model of gravastar is obtained in $D$-dimensional Einstein gravity. This class of solutions includes the gravastar as an alternative to D-dimensional versions of the Schwarzschild-Tangherlini black hole. The configuration of this new gravastar consists of three different regions with different equations of state: [I] Interior: 0 \leq r < r_1, ρ= -p; [II] Shell: r_1 \leq r < r_2, ρ= p; [III] Exterior: r_2 < r, ρ= p =0. The outer region of this gravastar corresponds to a higher dimensional Schwarzschild-Tangherlini black hole.

physics.gen-ph↗

arXiv2014

Nonommutative wormholes in $f(R)$ gravity

This paper discusses several new exact solutions of static wormholes in $f(R)$ gravity with a noncommutative-geometry background, which replaces point-like structures by smeared objects. In the first part of the paper we assume the power-law form $f(R)=aR^n$ and discuss several solutions corresponding to different values of the exponent. The second part of the paper assumes a particular form of the shape function that also yields a viable solution. This investigation generalizes some of our previous work in $f(R)$ gravity, as well as in noncommutative geometry.

gr-qc↗

arXiv2014

Exact interior solutions in (2 + 1) dimensional spacetime

We provide a new class of exact solutions for the interior in (2 + 1) dimensional spacetime. The solutions obtained for the perfect fluid model both with and without cosmological constant ($Λ$) are found to be regular and singularity free. It assume very simple analytical forms that help us to study the various physical properties of the configuration. Solutions without $Λ$ are found to be physically acceptable.

gr-qc↗

arXiv2014

Static Charged Fluid in (2+1)-Dimensions Admitting Conformal Killing Vectors

New solutions for $(2+1)$-dimensional Einstein-Maxwell space-time are found for a static spherically symmetric charged fluid distribution with the additional condition of allowing conformal killing vectors (CKV). We discuss physical properties of the fluid parameters. Moreover, it is shown that the model actually represents two structures, namely (i) Gravastar as an alternative of black hole and (ii) Electromagnetic Mass model depending on the nature of the equation state of the fluid. Here the gravitational mass originates from electromagnetic field alone. The solutions are matched with the exterior region of the Ba$\tilde{n}$ados-Teitelboim-Zanelli (BTZ) type isotropic static charged black hole as a consequence of junction conditions. We have shown that the central charge density is dependent on the value of $M_0$, the conserved mass of the BTZ black hole. This in turn depends on the black hole event horizon which again is related to the Hawking radiation temperature of a BTZ black hole. Thus one may have a clue that the central charge density is related with Hawking radiation temperature of the BTZ black hole on the exterior region of the static charged fluid sphere.

gr-qc↗

arXiv2014

Possible existence of wormholes in the galactic halo region

Two observational results, the density profile from simulations performed in the $Λ$CDM scenario and the observed flat galactic rotation curves, are taken as input with the aim of showing that the galactic halo possesses some of the characteristics needed to support traversable wormholes. This result should be sufficient to provide an incentive for scientists to seek observational evidence for wormholes in the galactic halo region.

gr-qc↗

arXiv2013

Noncommutative Wormholes in $f(R)$ Gravity with Lorentzian Distribution

In this paper, we derive some new exact solutions of static wormholes in $f(R)$ gravity supported by the matter possesses Lorentizian density distribution of a particle-like gravitational source. We derive the wormhole's solutions in two possible schemes for a given Lorentzian distribution: assuming an astrophysically viable $F(R)$ function such as a power-law form and discuss several solutions corresponding to different values of the exponent (here $F =\frac{df}{dR}$). In the second scheme, we consider particular form of two shape functions and have reconstructed f(R) in both cases. We have discussed all the solutions with graphical point of view.

gr-qc↗