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1.
An analysis of a spherically symmetric braneworld configuration is performed when the intrinsic curvature scalar is included
in the bulk action. In the case when the electric part of the Weyl tensor is zero, all the exterior solutions are found; one
of them is of the Schwarzschild-(A)dS
4 form, which is matched to a modified Oppenheimer-Volkoff interior solution. In the case when the electric part of the Weyl
tensor is non zero, the exterior Schwarzschild-(A)dS
4 black hole solution is modified receiving corrections from the non-local bulk effects. A non-universal gravitational constant
arises, depending on the density of the considered object and the Newton's law is modified for small and large distances;
however, the conventional limits are easily obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
In this paper, we investigate static cylindrically symmetric solution in metric f(R) gravity by taking matter in the form of dust. The assumption of constant Ricci scalar curvature is taken to find the solution.
The energy distribution of this solution is explored by applying Landau-Lifshitz energy-momentum complex. In addition, we
explore the stability as well as constant scalar curvature conditions for some viable f(R) models along with their energy distribution. It is interesting to mention here that these models satisfy the above mentioned
conditions. 相似文献
3.
《New Astronomy》2022
Our study illuminates the effects of gravitational collapse by considering heat flux anisotropic matter sources within the framework of the theory of gravity. We assume the non-static spherically symmetric configuration to narrate the nature of the interior spacetime and match it with the Vaidya exterior geometry. Further, we employ the well-known Karmarkar condition, as it reduces the solution-generating method of field equations to a single metric potential. To ensure the viability of our collapsing system, a comprehensive graphical analysis is presented in the context of the Logarithmic-corrected gravity model. Our investigation argues that there are no traces of trapped surfaces in the collapsing procedure. Thus, naked singularity and black hole are not the final fate of the gravitational collapse. 相似文献
4.
M. Farasat Shamir 《Astrophysics and Space Science》2010,330(1):183-189
The modified theories of gravity, especially the f(R) gravity, have attracted much attention in the last decade. In this context, we study the exact vacuum solutions of Bianchi
type I, III and Kantowski-Sachs spacetimes in the metric version of f(R) gravity. The field equations are solved by taking expansion scalar θ proportional to shear scalar σ which gives A=B
n
, where A and B are the metric coefficients. The physical behavior of the solutions has been discussed using some physical quantities. Also,
the function of the Ricci scalar is evaluated in each case. 相似文献
5.
The debate concerning the viability of f(R)-gravity as a natural extension of General Relativity could be realistically addressed by using results coming from binary pulsars like PSR 1913 + 16. To this end, we develop a quadrupolar approach to the gravitational radiation for a class of analytic f(R)-models. We show that experimental results are compatible with a consistent range of f(R)-models. This means that f(R)-gravity is not ruled out by the observations and gravitational radiation (in strong field regime) could be a test-bed for such theories. 相似文献
6.
In this paper, we search the existence of Bianchi type I cosmological model in f(R,T) gravity, where the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar R and of the trace of the stress-energy tensor T. We obtain the gravitational field equations in the metric formalism, and reconstruct the corresponding f(R,T) functions. Attention is attached to the special case, f(R,T)=f 1(R)+f 2(T) and two examples are assumed for this model. In the first example, we consider the unification of matter dominated and accelerated phases with f(R) gravity in anisotropic universe, and in the second instance, model of f(R,T) gravity with transition of matter dominated phase to the acceleration phase is obtained. In both cases, f(R,T) is proportional to a power of R with exponents depending on the input parameters. 相似文献
7.
In this paper, we analyze higher-dimensional spherical perfect fluid collapse in \(f(R,T)\) theory for minimally coupled models. We use Darmois junction conditions by taking Lemaître-Tolman-Bondi geometry as an interior region and Schwarzschild metric as an exterior spacetime. The solution of field equations is obtained for constant scalar curvature. We determine mass in two regions of the collapsing object and discuss the formation of apparent horizons. We conclude that modified curvature term tends to slow down the collapse rate. 相似文献
8.
K. Saaidi A. Vajdi S. W. Rabiei A. Aghamohammadi H. Sheikhahmadi 《Astrophysics and Space Science》2012,337(2):739-745
We introduce a new approach for investigating the weak field limit of vacuum field equations in f(R) gravity and we find the weak field limit of f(R)=R+μ
4/R gravity. Furthermore, we study the strong gravity regime in R+μ
4/R model of f(R) gravity. We show the existence of strong gravitational field in vacuum for such model. We find out in the limit μ→0, the weak field limit and the strong gravitational field can be regarded as a perturbed Schwarzschild metric. 相似文献
9.
This paper is devoted to study spherically symmetric shearfree charged gravitational collapse with radial heat flux and isotropic pressure. For the matching of the interior spacetime, we take Vaidya-Reissner-Nordström metric outside the spherical system. We solve the field equations numerically by taking ansatz on the metric functions and using Darmois junction conditions. The behavior of density, pressure, radial heat flux, luminosity and the mass function is analyzed. Finally, we check validity of the energy conditions through plots. 相似文献
10.
U. Kasper 《Astronomische Nachrichten》1976,297(3):127-129
We consider the inversion of a problem put by A. EINSTEIN and E. G. STRAUS , that is, we ask for restrictions on the scaling factor R(t) of the ROBERTSON WALKER metric and the functions H2(r') and A2(r') of a spherically symmetric and static vacuum metric, which are consequences of the requirement that the vacuum metric shall pass continuously differentiable into the ROBERTSON WALKER metric at a certain value rb of the comoving radial coordinate r. 相似文献
11.
In this study, we consider a flat Friedmann-Robertson-Walker (FRW) universe in the context of Palatini f(R) theory of gravity. Using the dynamical equivalence between f(R) gravity and scalar-tensor theories, we construct a point Lagrangian in the flat FRW spacetime. Applying Noether gauge symmetry approach for this f(R) Lagrangian we find out the form of f(R) and the exact solution for cosmic scale factor. It is shown that the resulting form of f(R) yield a power-law expansion for the scale factor of the universe. 相似文献
12.
This paper is devoted to investigate the spherically symmetric wormhole models in f(R, T) gravity, where T and R are trace of stress energy tensor and the Ricci scalar, respectively. In this context, we discuss three distinct cases of fluid distributions viz, anisotropic, barotropic and isotropic matter contents. After considering the exponential f(R, T) model, the behavior of energy conditions are analyzed that will help us to explore the general conditions for wormhole geometries in this gravity. It is inferred that the usual matter in the throat could obey the energy conditions but the gravitational field emerging from higher order terms of modified gravity favor the existence of the non-standard geometries of wormholes. The stability as well as the existence of wormholes are also analyzed in this theory. 相似文献
13.
In this paper, we solve the field equations in metric f(R) gravity for Bianchi type VI
0 spacetime and discuss evolution of the expanding universe. We find two types of non-vacuum solutions by taking isotropic
and anisotropic fluids as the source of matter and dark energy. The physical behavior of these solutions is analyzed and compared
in the future evolution with the help of some physical and geometrical parameters. It is concluded that in the presence of
isotropic fluid, the model has singularity at [(t)\tilde]=0\tilde{t}=0 and represents continuously expanding shearing universe currently entering into phantom phase. In anisotropic fluid, the
model has no initial singularity and exhibits the uniform accelerating expansion. However, the spacetime does not achieve
isotropy as t→∞ in both of these solutions. 相似文献
14.
We study the dynamical evolution of an f(R) model of gravity in a viscous and anisotropic background which is given by a Bianchi type-I model of the Universe. We find viable forms of f(R) gravity in which one is exactly the Einsteinian model of gravity with a cosmological constant and other two are power law f(R) models. We show that these two power law models are stable with a suitable choice of parameters. We also examine three potentials which exhibit the potential effect of f(R) models in the context of scalar tensor theory. By solving different aspects of the model and finding the physical quantities in the Jordan frame, we show that the equation of state parameter satisfy the dominant energy condition. At last we show that the two power law f(R) models behave like quintessence model at late times and also the shear coefficient viscosity tends to zero at late times. 相似文献
15.
B. C. Tewari 《Astrophysics and Space Science》2012,342(1):73-77
A new class of exact solutions of Einstein’s equations is proposed for a collapsing radiating spherically symmetric shear-free isotropic fluid undergoing radial heat flow. In remote past the solutions are static perfect fluid which then gradually starts evolving into radiating collapse. The interior solutions are matched with Vaidya exterior metric over the boundary. 相似文献
16.
We present a new model of dissipative energy fluid without appearance of horizon. The interior matter fluid is shear-free isotropic spherically symmetric and undergoing radial heat flow. The interior metric is matched with Vaidya exterior metric over the boundary. The model obeyed all the relevant physical and thermodynamic conditions. In this model, the collapse begins at infinite past with both infinite mass and radius and contracts to a point as time tends to zero without forming an event horizon. 相似文献
17.
N. Tomimura 《Astrophysics and Space Science》1993,201(2):223-228
The gravitational collapse of a slowly rotating star with small deviations from spherical symmetry is studied. The exterior metric is chosen to be the Kerr metric in synchronous coordinates discarding terms of order (a/r)2. Interior geometry is constructed by adding an off-diagonal term in first order ofa to the exact solution of the non-rotating case. This term is determined in part by requiring the validity of the junction conditions at the star's surface and by demanding that the angular momentum of the source is equal toM A, in agreement with the value measured by a distant observer. The resulting stress-energy tensor describes a homogeneous, pressureless, ideal fluid which rotates nonuniformly relative to the synchronous frame which is no longer comoving the stellar matter. 相似文献
18.
El-Nabulsi Ahmad?Rami 《Astrophysics and Space Science》2011,332(2):491-495
We investigate the late-time dynamics of a four-dimensional universe based on modified scalar field gravity in which the standard
Einstein-Hilbert action R is replaced by f(φ)R+f(R) where f(φ)=φ
2 and f(R)=AR
2+BR
μν
R
μν,(A,B)∈ℝ. We discussed two independent cases: in the first model, the scalar field potential is quartic and for this special form
it was shown that the universe is dominated by dark energy with equation of state parameter w≈−0.2 and is accelerated in time with a scale factor evolving like a(t)∝t
5/3 and B+3A≈0.036. When, B+3A→∞ which corresponds for the purely quadratic theory, the scale factor evolves like a(t)∝t
1/2 whereas when B+3A→0 which corresponds for the purely scalar tensor theory we found when a(t)∝t
1.98. In the second model, we choose an exponential potential and we conjecture that the scalar curvature and the Hubble parameter
vary respectively like
R=hH[(f)\dot]/f,h ? \mathbbRR=\eta H\dot{\phi}/\phi,\eta\in\mathbb{R} and
H=g[(f)\dot]c,(g,c) ? \mathbbRH=\gamma\dot{\phi}^{\chi},(\gamma,\chi)\in\mathbb{R}. It was shown that for some special values of χ, the universe is free from the initial singularity, accelerated in time, dominated by dark or phantom energy whereas the
model is independent of the quadratic gravity corrections. Additional consequences are discussed. 相似文献
19.
The focussing of gravitational radiation by the interior and exterior gravitational field of a Newtonian gravitational lens
is considered. A graphical method for determining the caustic structure of a Newtonian gravitational lens is presented and
the caustic structure of a solar type gravitational lens is discussed. Estimates of the amplitude magnification in the caustic
region indicate that waves with frequencies less than a critical cutoff frequency ω
c
are not amplified significantly. For a lens of massM this cutoff frequency is ω
c
≈(10-1πM)-1; for the Sun ω
c
≈104s-1.
Work supported in part by National Science Foundation Grant PHY78-05368. 相似文献