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Showing papers in "Astrophysics and Space Science in 2015"


Journal ArticleDOI
TL;DR: The 5th edition of the Roma-BZCAT Multifrequency Catalogue of Blazars is available in a printed version and online at the ASDC website ( http://www.asi.it/bzcat ) as mentioned in this paper.
Abstract: The 5th edition of the Roma-BZCAT Multifrequency Catalogue of Blazars is available in a printed version and online at the ASDC website ( http://www.asdc.asi.it/bzcat ); it is also in the NED database. It presents several relevant changes with respect to the past editions which are briefly described in this paper.

225 citations


Journal ArticleDOI
TL;DR: In this paper, the authors have used analytical solution of Krori and Barua metric to the Einstein field equations with anisotropic form of matter and power law model of f(G) gravity.
Abstract: This paper is devoted to study the possibility of forming anisotropic compact stars in modified Gauss–Bonnet, namely called as f(G) theory of gravity which is one of the strong candidates, responsible for the accelerated expansion of the universe. For this purpose, we have used analytical solution of Krori and Barua metric to the Einstein field equations with anisotropic form of matter and power law model of f(G) gravity. To determine the unknown constants in Krori and Barua metric, we have used the sample of compact stars, 4U1820-30, Her X-1, SAX J 1808-3658. The physical behavior of these stars have been analyzed with the observational data. In this setting, we have checked all the regularity conditions and stability of the compact stars 4U1820-30, Her X-1, SAX J 1808-3658.

117 citations


Journal ArticleDOI
TL;DR: In this paper, a modified theory of gravity f(R,T), where R and T are the Ricci scalar and the trace of the energy momentum tensor, respectively, is presented.
Abstract: In this paper we undertake the modified theory of gravity f(R,T), where R and T are the Ricci scalar and the trace of the energy momentum tensor, respectively. Imposing the conservation of the energy momentum tensor, we obtain a model about what dynamics and stability are studied. The stability is developed using the de Sitter and power-law solutions. The results show that the model presents stability for both the de Sitter and power-law solutions. Regarding the dynamics, cosmological solutions are obtained by integrating the background equations for both the low-redshift and high-redshift regimes and are consistent with the observational data.

99 citations


Journal ArticleDOI
TL;DR: In this paper, the behavior of static spherically symmetric relativistic objects with locally anisotropic matter distribution considering the Tolman VII form for the gravitational potential in curvature coordinates was studied.
Abstract: In this paper we have studied the behavior of static spherically symmetric relativistic objects with locally anisotropic matter distribution considering the Tolman VII form for the gravitational potential $g_{rr}$ in curvature coordinates together with the linear relation between the energy density and the radial pressure. The interior spacetime has been matched continuously to the exterior Schwarzschild geometry. We have investigated and analyzed different physical properties of the stellar model and presented graphically.

91 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the properties of the youngest (10-20mm) A-star debris disks to consider the transition from protoplanetary to debris disk, and the physical distinction between these two classes should rest on the presence of primordial gas in sufficient quantities to dominate the motion of small dust grains (rather than on the secondary nature of the dust or its level of stirring).
Abstract: The protoplanetary disks seen around Herbig Ae stars eventually dissipate leaving just a tenuous debris disk, comprised of planetesimals and the dust derived from them, as well as possibly gas and planets. This paper uses the properties of the youngest (10–20 Myr) A star debris disks to consider the transition from protoplanetary to debris disk. It is argued that the physical distinction between these two classes should rest on the presence of primordial gas in sufficient quantities to dominate the motion of small dust grains (rather than on the secondary nature of the dust or its level of stirring). This motivates an observational classification based on the dust emission spectrum which is empirically defined so that A star debris disks require fractional excesses <3 at 12 μm and <2000 at 70 μm. We also propose that a useful hypothesis to test is that the planet and planetesimal systems seen on the main sequence are already in place during the protoplanetary disk phase, but are obscured or overwhelmed by the rest of the disk. This may be only weakly true if the architecture of the planetary system continues to change until frozen at the epoch of disk dispersal, or completely false if planets and planetesimals form during the relatively short dispersal phase. Five steps in the transition are discussed: (i) the well-known carving of an inner hole to form a transition disk; (ii) depletion of mm-sized dust in the outer disk, where it is noted that it is of critical importance to ascertain whether this mass ends up in larger planetesimals or is collisionally depleted; (iii) final clearing of inner regions, where it is noted that multiple debris-like mechanisms exist to replenish moderate levels of hot dust at later phases, and that these likely also operate in protoplanetary disks; (iv) disappearance of the gas, noting the recent discoveries of both primordial and secondary gas in debris disks which highlight our ignorance in this area and its impending enlightenment by ALMA; (v) formation of ring-like structure of planetesimals, noting that these are shaped by interactions with planets, and that the location of the planetesimals in protoplanetary disks may be unrelated to that of dust concentrations therein that are set by gas interactions.

88 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present an analytical study on the dynamics of a third body in the restricted three-body problem and find an appropriate approximation for the locations of the out-ofplane equilibrium points in the special case of a nonisotropic variation of the mass.
Abstract: This work aims to present an analytical study on the dynamics of a third body in the restricted three-body problem. We study this model in the context of the third body having variable-mass changes according to Jeans’ law. The equation of motion is constructed when the variation of the mass is non-isotropic. We find an appropriate approximation for the locations of the out-of-plane equilibrium points in the special case of a non-isotropic variation of the mass. Moreover, some graphical investigations are shown for the effects of the parameters which characterize the variable mass on the locations of the out-of-plane equilibrium points, the regions of possible and forbidden motions of the third body. This model has many applications, especially in the dynamics behavior of small objects such as cosmic dust and grains. It also has interesting applications for artificial satellites, future space colonization or even vehicles and spacecraft parking.

82 citations


Journal ArticleDOI
Piyali Bhar1
TL;DR: In this article, a new model of anisotropic stars corresponding to the exterior Schwarzschild metric was proposed, where the Einstein field equations have been solved by utilizing the Krori-Barua (KB) ansatz (Krori and Barua in J. Phys. A, Math. Gen. 8:508, 1975).
Abstract: Present paper provides a new model of anisotropic strange star corresponding to the exterior Schwarzschild metric. The Einstein field equations have been solved by utilizing the Krori-Barua (KB) ansatz (Krori and Barua in J. Phys. A, Math. Gen. 8:508, 1975) in presence of quintessence field characterized by a parameter ω q with $-1<\omega_{q}<-\frac{1}{3}$ . The obtained solutions are free from central singularity. Our model is potentially stable. The numerical values of mass of the different strange stars SAXJ1808.4-3658(SS1) (radius=7.07 km), 4U1820-30 (radius=10 km), Vela X-12 (radius=9.99 km), PSR J 1614-2230 (radius=10.3 km) obtained from our model is very close to the observational data that confirms the validity of our proposed model. The interior solution is also matched to the exterior Schwarzschild spacetime in presence of thin shell where negative surface pressure is required to hold the thin shell against collapsing.

79 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of strong magnetic fields in models involving quadratic and cubic corrections in the Ricci scalar R to the Hilbert-Einstein action is investigated.
Abstract: Neutron stars with strong magnetic fields are considered in the framework of f(R) gravity. In order to describe dense matter in magnetic field, the model with baryon octet interacting through σρω-fields is used. The hyperonization process results in softening the equation of state (EoS) and in decreasing the maximal mass. We investigate the effect of strong magnetic field in models involving quadratic and cubic corrections in the Ricci scalar R to the Hilbert–Einstein action. For large fields, the Mass–Radius relation differs considerably from that of General Relativity only for stars with masses close to the maximal one. Another interesting feature is the possible existence of more compact stable stars with extremely large magnetic fields (∼6×1018 G instead of ∼4×1018 G as in GR) in the central regions of the stars. Due to cubic terms, a significant increasing of the maximal mass is possible.

79 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated whether or not the Big Rip can be avoided in the locally rotationally symmetric (LRS) Bianchi type-I cosmological models in f(R,T) theory of gravity.
Abstract: The locally rotationally symmetric (LRS) Bianchi type-I cosmological models have been investigated in f(R,T) theory of gravity, where R is the Ricci scalar and T is the trace of the energy momentum tensor, for some choices of the functional f(R,T)=f 1(R)+f 2(T). The exact solutions of the field equations are obtained for the linearly varying deceleration parameter q(t) proposed by Akarsu and Dereli (2012). Keeping an eye on the accelerating nature of the universe in the present epoch, the dynamics and physical behaviour of the models have been discussed. It is interesting to note that in one of the model, the universe ends with a big rip. By taking different functional forms for f 2(T) we have investigated whether or not the Big Rip can be avoided. We found that, the Big Rip situation can not be avoided and may be inherent in the linearly varying deceleration parameter. We have also applied the State-finder diagnostics to get the geometrical dynamics of the universe at different phases.

76 citations


Journal ArticleDOI
TL;DR: In this paper, the authors constrain two non-flat time-evolving dark energy cosmological models by using Hubble parameter data, Type Ia supernova apparent magnitude measurements, and baryonic acoustic oscillation peak length scale observations.
Abstract: We constrain two non-flat time-evolving dark energy cosmological models by using Hubble parameter data, Type Ia supernova apparent magnitude measurements, and baryonic acoustic oscillation peak length scale observations. The inclusion of space curvature as a free parameter in the analysis results in a significant broadening of the allowed range of values of the parameter that governs the time evolution of the dark energy density in these models. While consistent with the “standard” spatially-flat ΛCDM cosmological model, these data are also consistent with a range of mildly non-flat, slowly time-varying dark energy models. After marginalizing over all other parameters, these data require the averaged magnitude of the curvature density parameter |Ω k0|≲0.15 at 1σ confidence.

75 citations


Journal ArticleDOI
TL;DR: In this paper, the authors provided new exact solutions to the Einstein-Maxwell system of equations for matter configurations with anisotropy and charge, where the spacetime is static and spherically symmetric.
Abstract: We provide new exact solutions to the Einstein-Maxwell system of equations for matter configurations with anisotropy and charge. The spacetime is static and spherically symmetric. A quadratic equation of state is utilised for the matter distribution. By specifying a particular form for one of the gravitational potentials and the electric field intensity we obtain new exact solutions in isotropic coordinates. In our general class of models, an earlier model with a linear equation of state is regained. For particular choices of parameters we regain the masses of the stars PSR J1614-2230, 4U 1608-52, PSR J1903+0327, EXO 1745-248 and SAX J1808.4-3658. A comprehensive physical analysis for the star PSR J1903+0327 reveals that our model is reasonable.

Journal ArticleDOI
TL;DR: In this paper, a new model of an anisotropic star which admits the Chaplygin equation of state is proposed, where the exterior spacetime is described by a Schwarzschild line element.
Abstract: In the present paper we propose a new model of an anisotropic strange star which admits the Chaplygin equation of state. The exterior spacetime is described by a Schwarzschild line element. The model is developed by assuming the Finch–Skea ansatz (Finch and Skea in Class. Quantum Gravity 6:467, 1989). We obtain the model parameters in closed form. Our model is free from a central singularity. Choosing some particular values for the parameter we show that our model corroborates the observational data of the strange star PSR J1614-2230 (Gangopadhyay et al. in Mon. Not. R. Astron. Soc. 431:3216, 2013).

Journal ArticleDOI
TL;DR: In this paper, the authors explored two ideas: (1) a statistical search for a possible third, intermediate category of bursts (between the short and the long) among 2041 BATSE GRBs and 757 Swift/BAT ones; (2) a study of bursts' intrinsic durations, where durations in the bursts' reference frames (instead of the observed durations) are considered; for this, 248 Swift/ BAT bursts that have redshift measurements were statistically analyzed for the same categorization goal.
Abstract: Studies of BATSE bursts (Kouveliotou et al. 1993) have resulted in the widespread adoption of a two-group categorization: long bursts (those with durations ≥2 seconds) and short bursts (those with durations ≤2 seconds). This categorization, one must recall, used the observed T 90 time durations for bursts (during which 90 % of a burst’s fluence is measured). In this work, we have explored two ideas: (1) a statistical search for a possible third, intermediate category of bursts (between the “short” and the “long” ones) among 2041 BATSE GRBs and 757 Swift/BAT ones; (2) a study of bursts’ intrinsic durations, where durations in the bursts’ reference frames (instead of the observed durations) are considered; for this, 248 Swift/BAT bursts that have redshift measurements were statistically analyzed for the same categorization goal. We first use a Monte Carlo method to determine the proper binning of each GRB, considering that bursts come with different uncertainties on their durations. Then, using the method of minimization of chi-square χ 2, we search for the best fit of the normalized frequency distributions $\frac{1}{N_{0}}\frac{dN}{d\ln{T}}$ of durations; this allows us to compare fits with two groups (“short” and “long”) with fits with three groups (“short”, “long”, and “intermediate”). Our results indicate that the distributions of observed durations are better fitted by three groups than two groups for Swift/BAT data; interestingly, the “intermediate” group appears rather clearly for both observed and intrinsic durations. For BATSE data, the statistical test does not prefer three groups over two. We discuss the results, their possible underlying causes, and reasonable interpretations.

Journal ArticleDOI
TL;DR: In this paper, the role of adiabatic index (stiffness parameter) on the evolution of an anisotropic collapsing spherical self-gravitating system in Palatini f(R) gravity was studied.
Abstract: The purpose of this paper is to study role of adiabatic index (stiffness parameter) on the evolution of an anisotropic collapsing spherical self-gravitating system in Palatini f(R) gravity. In this scenario, we construct dynamical equation with the help of contracted Bianchi identities of the effective dark sources as well as usual matter. The perturbation approach is applied on the physical variables which consequently perturbes the Ricci scalar. We discuss instabilities both for zero and non-zero expansion. It is shown that instability range of the given system depends upon energy density profile, anisotropic pressure and chosen f(R) model in both scenarios. However, the adiabatic index is not helpful in expansion-free instability analysis at N and pN regimes.

Journal ArticleDOI
TL;DR: In this article, stability analysis of spherically symmetric collapsing star surrounding in locally anisotropic environment in f(R,T) gravity, where R is Ricci scalar and T corresponds to the trace of energy momentum tensor.
Abstract: This work is based on stability analysis of spherically symmetric collapsing star surrounding in locally anisotropic environment in f(R,T) gravity, where R is Ricci scalar and T corresponds to the trace of energy momentum tensor. Field equations and dynamical equations are presented in the context of f(R,T) gravity. Perturbation scheme is employed on dynamical equations to find the collapse equation. Furthermore, condition on adiabatic index Γ is constructed for Newtonian and post-Newtonian eras to address instability problem. Some constraints on physical quantities are imposed to maintain stable stellar configuration. The results in this work are in accordance with f(R) gravity for specific case.

Journal ArticleDOI
TL;DR: In this article, it was shown that gravitino particles from the traversable Lorentzian wormholes (TLWH) reveal a negative Hawking temperature (HT) in the past outer trapping horizon geometry (POTHG) and derived the Rarita-Schwinger equations for that geometry.
Abstract: Recent research shows that Hawking radiation (HR) is also possible around the trapping horizon of a wormhole. In this article, we show that the HR of gravitino (spin- $3/2$ ) particles from the traversable Lorentzian wormholes (TLWH) reveals a negative Hawking temperature (HT). We first introduce the TLWH in the past outer trapping horizon geometry (POTHG). Next, we derive the Rarita-Schwinger equations (RSEs) for that geometry. Then, using both the Hamilton-Jacobi (HJ) ansatz and the WKB approximation in the quantum tunneling method, we obtain the probabilities of the emission/absorption modes. Finally, we derive the tunneling rate of the emitted gravitino particles, and succeed to read the HT of the TLWH.

Journal ArticleDOI
TL;DR: In this article, a set of exact spherically symmetric solutions describing the interior of a relativistic star under modified gravity were provided. But they assume the existence of a conformal Killing vector field within this modified gravity.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, a new class of solutions to the Einstein's field equations corresponding to a static spherically symmetric anisotropic system by generalizing the ansatz of Finch and Skea was presented.
Abstract: We present a new class of solutions to the Einstein’s field equations corresponding to a static spherically symmetric anisotropic system by generalizing the ansatz of Finch and Skea [Class. Quantum Grav. 6:467, 1989] for the gravitational potential g rr . The anisotropic stellar model previously studied by Sharma and Ratanpal [Int. J. Mod. Phys. D 13:1350074, 2013] is a sub-class of the solutions provided here. Based on physical requirements, regularity conditions and stability, we prescribe bounds on the model parameters. By systematically fixing values of the model parameters within the prescribed bound, we demonstrate that our model is compatible with the observed masses and radii of a wide variety of compact stars like 4U 1820-30, PSR J1903+327, 4U 1608-52, Vela X-1, PSR J1614-2230, SAX J1808.4-3658 and Her X-1.

Journal ArticleDOI
TL;DR: In this paper, the authors derived the Zkharov-Kuznetsov (ZK) equation for nonlinear ion-acoustic travelling waves propagating in a three-dimensional multicomponent magnetoplasma system composed of positive ions, negative ions and superthermal electrons.
Abstract: Properties of nonlinear ion-acoustic travelling waves propagating in a three-dimensional multicomponent magnetoplasma system composed of positive ions, negative ions and superthermal electrons are considered. Using the reductive perturbation technique (RPT), the Zkharov-Kuznetsov (ZK) equation is derived. The bifurcation theory of planar dynamical systems is applied to investigate the existence of the solitary wave solutions and the periodic travelling wave solutions of the resulting ZK equation. It is found that both compressive and rarefactive nonlinear ion-acoustic travelling waves strongly depend on the external magnetic field, the unperturbed positive-to-negative ions density ratio, the direction cosine of the wave propagation vector with the Cartesian coordinates, as well as the superthermal electron parameter. The present model may be useful for describing the formation of nonlinear ion-acoustic travelling wave in certain astrophysical scenarios, such as the D and F-regions of the Earth’s ionosphere.

Journal ArticleDOI
TL;DR: In this paper, the authors connect the rotating mass dipole with natural elongated bodies, including asteroids and comets, to obtain five parameters of the dipole model, including the mass ratio, system mass, spinning period, characteristic distance and the ratio between the gravitational and centrifugal forces.
Abstract: The focus of this paper is to connect the rotating mass dipole with natural elongated bodies. The dipole system is consisted with two point masses connected with a massless rod in a constant characteristic distance. A brief introduction on the dynamics near the rotating mass dipole is given with the distribution of its equilibrium points and zero-velocity curves. Five parameters of the dipole model are required to approximate the potential distribution of an elongated body out of the body’s surface, including the mass ratio, system mass, spinning period, characteristic distance and the ratio between the gravitational and centrifugal forces. The method to obtain the five parameters is presented along with its application to the asteroid 1620 Geographos in detail. The accuracy of the dipole model is quantified with the relative tolerance of locations of the equilibrium points. Six more elongated asteroids and comets, such as 25143 Itokawa and 103P/Hartley-2, are illustrated to provide a reference for further studies. Model justification is evaluated through comparison between sample elongated bodies and their corresponding dipole models with regard to the external potential distribution, the stability and topological manifold structure of the equilibrium points.

Journal ArticleDOI
TL;DR: In this article, the equations of motion in f(T) theory with a static spherically symmetric spacetime in the presence of anisotropic fluid and quintessence field have been solved by using Krori-Barua metric.
Abstract: This paper deals with the new theoretical model of quintessence anisotropic star in f(T) theory of gravity. The equations of motion in f(T) theory with a static spherically symmetric spacetime in the presence of anisotropic fluid and quintessence field have been solved by using Krori-Barua metric. In this case, we have used the diagonal tetrad field that leads to a linear form f(T) function. We have determined that all the obtained solutions are free from central singularity and potentially stable. The values of the unknown constants existing in Krori and Barua metric have been calculated by using the observed values for mass of the different strange stars PSR J 1614-2230, SAXJ1808.4-3658(SS1), 4U1820-30, PSR J 1614-2230. The physical parameters (anisotropy, stability and redshift) of the stars have been investigated in detail. We have determined the constraint under which results of f(T), theory reduces to general relativity.

Journal ArticleDOI
Piyali Bhar1
TL;DR: In this paper, a new model of hybrid star with strange quark matter along with normal baryonic matter is presented, which is based on the MIT bag model equation of state.
Abstract: Present paper provides a new model of hybrid star with strange quark matter along with normal baryonic matter. The relation between pressure and density of the quark matter is given by the MIT bag model equation of state. The model is developed in the framework of Krori and Barua (KB) ansatz (Krori and Barua, Phys. A, Math. Gen. 8:508, 1975). All the physical requirements are satisfied by our model. The value of mass calculated from our model is close to the observational data which gives the validity of our present model. We match our interior solution to the exterior Schwarzschild metric where negative surface pressure is required to hold the thin shell against collapsing.

Journal ArticleDOI
TL;DR: In this article, the existence of stars in a tetrad field of static spacetime with charged anisotropic fluid and the MIT bag model has been analyzed by assuming the parametric form of the metric functions in terms of the radial profiles with some unknown constant (introduced by Krori and Barua).
Abstract: This paper deals with the existence of strange stars in $f(T)$ modified gravity. For this purpose, we have taken the diagonal tetrad field of static spacetime with charged anisotropic fluid and the MIT bag model, which provide the linear relation between radial pressure and density of the matter. Further, the analysis of the resulting equations have been done by assuming the parametric form of the metric functions in terms of the radial profiles with some unknown constant (introduced by Krori and Barua). By the matching of two metrics, the unknown constant of the metric functions appears in terms of the mass, radius and charge of the stars. The observed values of these quantities have been used for detailed analysis of the derived model. We have discussed the regularity, anisotropy, energy conditions, stability and surface redshift of the model.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss dynamical properties of dissipative collapsing cylindrical self-gravitating systems with account of f(R) = R+γR 2+βρ 1 /βρ 2/βρ 3 gravity model.
Abstract: In this paper, we discuss dynamical properties of dissipative collapsing cylindrical self-gravitating systems with account of f(R)=R+γR 2+β 1 R 3 gravity model. In this perspective, we see effects of higher curvature terms in the formulations of structure scalars already obtained from the orthogonal decomposition of Weyl curvature scalar in general relativity. We compute mass function by generalizing Misner-Sharp formalism and discuss the contribution of relaxation time in the radiating collapsing process. The contribution of scalar functions in the modeling of static anisotropic as well as isotropic fluid configurations are explored. We conclude that all static anisotropic cylindrical solutions of f(R) field equations can be written explicitly by means of triplet of these scalar functions.

Journal ArticleDOI
TL;DR: In this article, the authors investigated cosmological models with two interacting fluids: dark energy and dark matter in flat Friedmann-Robertson-Walker universe and obtained analytic representation for characteristic properties, in particular the bulk viscosity ζ=ζ(H,t) as function of Hubble parameter and time.
Abstract: We investigate cosmological models with two interacting fluids: dark energy and dark matter in flat Friedmann-Robertson-Walker universe. The interaction between dark energy and dark matter is described in terms of the parameters present in the inhomogeneous equation of state when allowance is made for bulk viscosity, for the Little Rip, the Pseudo Rip, and the bounce universes. We obtain analytic representation for characteristic properties in these cosmological models, in particular the bulk viscosity ζ=ζ(H,t) as function of Hubble parameter and time. We discuss the corrections of thermodynamical parameters in the equations of state due coupling between the viscous fluid and dark matter. Some common properties of these corrections are elucidated.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the null geodesics and all kinds of orbits corresponding to the energy levels for the Schwarzschild-anti de Sitter black hole surrounded by quintessence with the effective potential for the photons.
Abstract: In this paper, by using the effective potential for the photons, we analysis the null geodesics and all kinds of orbits corresponding to the energy levels for the Schwarzschild-anti de Sitter black hole surrounded by quintessence with \(\omega_{q}= -\frac{2}{3}\) and compare our results with those obtained for the Schwarzschild black hole surrounded by quintessence matter We also investigate the circular orbits and calculate the angle of deflection of the photons

Journal ArticleDOI
TL;DR: In this paper, the Friedmann-Robertson-Walker universe containing viscous fluid and matter creation is considered in the modified f(R,T) theory of gravitation, which is an arbitrary function of the Ricci scalar R and the trace T of the energy-momentum tensor.
Abstract: The Friedmann–Robertson–Walker Universe containing viscous fluid and matter creation is considered in the modified f(R,T) theory of gravitation, which is an arbitrary function of the Ricci scalar R and the trace T of the energy-momentum tensor. We assume the bulk viscosity and the matter creation as two independent processes as discussed by Progogine et al. (1988, 1989). The effects of bulk viscosity and matter creation are investigated by considering the general form of bulk viscous coefficient ζ=ζ 0+ζ 1 H and particle creation rate Γ(t)=3βH. Assuming a particular class of f(R,T)=R+2f(T), where f(T)=αT, various forms of the scale factor are obtained with constant and time-dependent bulk viscous coefficient using equation of state p=(γ−1)ρ. All possible (deceleration, acceleration and their transitions) evolutions of the Universe are discussed by constraining the models on β, ζ 0 and ζ 1 in case of time-dependent deceleration parameter for positive and negative values of α. A big-rip singularity is observed for γ<0 at a finite value of cosmic time with some restrictions on parameters. It is also noted that the finite time big-rip singularity can be removed for a specific range of α in phantom region. The role of bulk viscosity and matter creation are discussed in detail through the tables and graphs of variation of deceleration parameter and the scale factor.

Journal ArticleDOI
TL;DR: In this article, the authors explore the behaviors of scalar field in modified f(R,T) gravity theory within the framework of a flat Friedmann-Robertson-Walker cosmological model.
Abstract: In this paper, we explore the behaviors of scalar field in modified f(R,T) gravity theory within the framework of a flat Friedmann-Robertson-Walker cosmological model. The universe is assumed to be filled with two non-interacting matter sources, scalar field (normal or phantom) with scalar potential and matter contribution due to f(R,T) action. We first explore a model where the potential is a constant, and the universe evolves as a de Sitter type. This model is compatible with phantom scalar field only which gives fine tuning with the recent observations. The model exhibits a wide variety of early time physical phenomena that eventually behaves like a cosmological constant at late times. The model shows transition from decelerated to accelerated expansion of the universe. We also explore a model where the scalar field potential and the scale factor evolve exponentially as a scalar field. This model is compatible with normal scalar field only and describes transition from inflationary to the decelerated phase at early times and quintessence to phantom phase at late times. We constraint our results with the recent observational data and find that some values of parameters are consistent with SNe Ia and H(z)+SNe Ia data to describe accelerated expansion only whereas some one give decelerated and accelerated expansions with H(z), WMAP7 and WMAP7+BAO+H(z) observational data.

Journal ArticleDOI
TL;DR: In this article, the equations of motion in f(T) theory with a static spherically symmetric spacetime in the presence of anisotropic fluid and quintessence field have been solved by using Krori-Barua metric.
Abstract: This paper deals with the new theoretical model of quintessence anisotropic star in f(T) theory of gravity. The equations of motion in f(T) theory with a static spherically symmetric spacetime in the presence of anisotropic fluid and quintessence field have been solved by using Krori-Barua metric. In this case, we have used the diagonal tetrad field that leads to a linear form f(T) function. We have determined that all the obtained solutions are free from central singularity and potentially stable. The values of the unknown constants existing in Krori and Barua metric have been calculated by using the observed values for mass of the different strange stars PSR J 1614-2230, SAXJ1808.4-3658(SS1), 4U1820-30, PSR J 1614-2230. The physical parameters (anisotropy, stability and redshift) of the stars have been investigated in detail. We have determined the constraint under which results of f(T), theory reduces to general relativity.

Journal ArticleDOI
TL;DR: In this article, the authors apply the ASTG-model to the observed secular trend in the mean Sun-(Earth-Moon) and Earth-Moon distances thereby providing an alternative explanation as to what the cause of this secular trend may be.
Abstract: We here apply the ASTG-model to the observed secular trend in the mean Sun-(Earth-Moon) and Earth-Moon distances thereby providing an alternative explanation as to what the cause of this secular trend may be. Within the margins of observational error; for the semi-major axis rate of the Earth-Moon system, in agreement with observations (of Standish and Kurtz, Proceedings IAU Colloquium, IAU, pp. 163–179, Cambridge University Press, Cambridge, 2005), we obtain a value of about +(5.10±0.10) cm/yr. The ASTG-model predicts orbital drift as being a result of the orbital inclination and the Solar mass loss rate. The Newtonian gravitational constant G is assumed to be an absolute time constant. Krasinsky and Brumberg (Celest. Mech. Dyn. Astron. 90(3–4):267–288, 2004); Standish and Kurtz (2005) reported for the Earth-Moon system, an orbital recession from the Sun of about +(15.00±4.00) cm/yr and +(7.00±2.00) cm/yr respectively; while Williams et al. (Phys. Rev. Lett. 93:261101, 2004); Williams and Boggs (Proceedings of 16th International Workshop on Laser Ranging, Space Research Centre, Polish Academy of Sciences, Poland, 2009), Williams et al. (Planet. Sci. 3(1):2, 2014) report for the Moon, a semi-major axis rate of about +(38.08±0.04) mm/yr from the Earth. The predictions of the ASTG-model for the Earth-Moon system agrees very well with those the findings of Standish and Kurtz (2005), Krasinsky and Brumberg (2004). The lost orbital angular momentum for the Earth-Moon system—which we here hypothesize to be gained as spin by the two body Earth-Moon system; this lost angular momentum accounts very well for the observed Lunar drift, therefore, one can safely say that the ASTG-model does to a reasonable degree of accuracy predict the observed Lunar semi-major axis rate of about +(38.08±0.04) mm/yr from the Earth.