共查询到20条相似文献，搜索用时 31 毫秒
1.
As a generalization of the Brans-Dicke type scalar-tensor gravity in a braneworld context, we study cosmological phase space of a braneworld model with induced gravity in the presence of a scalar field on the brane. We consider a quintom field minimally or non-minimally coupled to induced gravity on the warped DGP brane and we present a detailed analysis of the critical points, their stability and late-time cosmological viability of the solutions within a phase space approach. In particular, de Sitter solutions, different from the famous self-accelerated branch of the DGP model are found and the phase-space analysis for checking their attractor properties is performed. We analyze also the possibility of crossing of the phantom divide by the effective equation of state parameter of the model. We also focus on the classical stability of the solutions in w–w′ phase plane. 相似文献
2.
Marcelo Samuel Berman 《Astrophysics and Space Science》2007,311(4):359-361
Pathria (1972) has shown, for a pressureless closed Universe, that it is inside a black (or white) hole. We show now, that the Universe
with a cosmic pressure obeying Einstein’s field equations, can be inside a white-hole. In the closed case, a positive cosmological
constant does the job; for the flat and open cases, the condition we find is not verified for the very early Universe, but
with the growth of the scale-factor, the condition will be certainly fulfilled for a positive cosmological constant, after
some time. We associate the absolute temperature of the Universe, with the temperature of the corresponding white-hole. 相似文献
3.
We study the late-time cosmological viability of the solutions in the DGP braneworld scenario. We consider a quintessence field trapped on the normal branch of the DGP model and we suppose this scalar field is both minimally and non-minimally coupled to induced gravity on the brane. Since a successful cosmological model should therefore admit for a sequence of epochs: a radiation era, a sufficiently long matter dominated era and a final stable positively accelerated scaling solution, we analyze the cosmological properties of system in its critical points. 相似文献
4.
We study the effects of the non-minimal coupling on the dissipative dynamics of the warm inflation in a braneworld setup,
where the inflaton field is non-minimally coupled to induced gravity on the warped DGP brane. A warped DGP scenario is a hybrid
model containing both DGP and RSII character. We study with details the effects of the non-minimal coupling and dissipation
on the inflationary dynamics on the normal DGP branch of this hybrid scenario in the high-dissipation and high-energy regime. We show that incorporation of the non-minimal coupling
in this setup decreases the number of e-folds relative to the minimal case. We also compare our model parameters with recent
observational data. 相似文献
5.
Capture cross section of magnetized particle (with nonzero magnetic moment) by braneworld black hole in uniform magnetic field
is studied. The magnetic moment of particle was chosen as it was done by de Felice and Sorge (Class. Quantum Gravity 20:469,
2003) and for the simplicity particle with zero electric charge is chosen. It is shown that the spin of particle as well as the
brane parameter are to sustain the stability of particles circularly orbiting around the black hole in braneworld i.e. spin
of particles and brane parameter try to prevent the capture by black hole. 相似文献
6.
LRS Bianchi type-I dark energy model with variable equation of state (EoS) parameter is presented in the scalar-tensor theory
of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). To get a determinate solution of the field equations we take the help of special law of variation for Hubble’s parameter
presented by Bermann (Nuovo Cimento B 74:182, 1983) which yields a cosmological model with negative constant deceleration parameter. Some physical and kinematical properties
of the model are also discussed. 相似文献
7.
In this paper we present a class of non-stationary solutions of Einstein’s field equations describing embedded Vaidya-de Sitter black holes with a cosmological variable function Λ(u). The Vaidya-de Sitter black hole is interpreted as the radiating Vaidya black hole is embedded into the non-stationary de Sitter space with variable Λ(u). The energy-momentum tensor of the Vaidya-de Sitter black hole is expressed as the sum of the energy-momentum tensors of the Vaidya null fluid and that of the non-stationary de Sitter field, and satisfies the energy conservation law. We study the energy conditions (like weak, strong and dominant conditions) for the energy-momentum tensor. We find the violation of the strong energy condition due to the negative pressure and leading to a repulsive gravitational force of the matter field associated with Λ(u) in the space-time. We also find that the time-like vector field for an observer in the Vaidya-de Sitter space is expanding, accelerating, shearing and non-rotating. It is also found that the space-time geometry of non-stationary Vaidya-de Sitter solution with variable Λ(u) is Petrov type D in the classification of space-times. We also find the Vaidya-de Sitter black hole radiating with a thermal temperature proportional to the surface gravity and entropy also proportional to the area of the cosmological black hole horizon. 相似文献
8.
A version of the virial theorem is derived in a brane-world scenario in the framework of a warped DGP model where the action on the brane is an arbitrary function of the Ricci scalar, $\mathcal{L}(R)$ . The extra terms in the modified Einstein equations generate an equivalent mass term (geometrical mass), which give an effective contribution to the gravitational energy and offer viable explanation to account for the virial mass discrepancy in clusters of galaxies. We also obtain the radial velocity dispersion of galaxy clusters and show that it is compatible with the radial velocity dispersion profile of such clusters. Finally, we compare the result of the model with $\mathcal{L}(R)$ gravity theories. 相似文献
9.
Assuming spherical symmetry we analyse the dynamics of an inhomogeneous dark radiation vaccum on a Randall and Sundrum 3-braneworld.
Under certain natural conditions we show that the effective Einstein equations on the brane form a closed system. On a de
Sitter brane and for negative dark energy density we determine exact dynamical and inhomogeneous solutions which depend on
the brane cosmological constant, on the dark radiation tidal charge and on its initial configuration. We also identify the
conditions leading to the formation of a singularity or of regular bounces inside the dark radiation vaccum.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
A. A. Saharian 《Astrophysics》2005,48(1):122-133
The vacuum expectations of the surface energy-momentum tensor generated on a brane in AdS space-time by quantum fluctuations of a scalar field with an arbitrary coupling parameter are studied. It is assumed that the field satisfies mixed boundary conditions on the brane. A generalized zeta function method is used as a regularization procedure. Two regions, located to the left (L-region) and right (R-region) of the brane, are considered. It is shown that the surface energies for both these regions contain pole and finite contributions. Analytic expressions are derived for both parts. When calculating the total surface energy including the contributions from the L- and R-regions, the pole terms add out in odd spatial dimensions. The surface energy-momentum tensor induced by vacuum quantum effects corresponds to the generation of a cosmological constant on the brane. These results are applied to the second Randall-Sundrum model.Translated from Astrofizika, Vol. 48, No. 1, pp. 151–164 (February 2005). 相似文献
11.
Cosmological electrovac field equations are studied in Bertotti-Robinson-type space-time, and a class of cosmological solutions is obtained. The nature of the electromagnetic fields and singularities of the solution is studied. A technique is established to generate these solutions from a known vacuum solution with a non-zero cosmological constant. 相似文献
12.
We investigate the influence of the cosmological constant, Λ, on the bending of light by a charged black hole in a de Sitter spacetime. Despite vanishing of the cosmological constant in the second order null geodesic equation, considering the method introduced by Rindler and Ishak (2007), we obtain an expression for the deflection angle, consistent with previous results for Schwarzschild, Schwarzschild-de Sitter (SdS), and Reissner-Nordstrom (RN) spacetimes. 相似文献
13.
Exact solution of Einstein’s field equations is obtained for massive string cosmological model of Bianchi III space-time using
the technique given by Letelier (Phys. Rev. D 20:2414, 1983) in presence of perfect fluid and decaying vacuum energy density Λ. To get the deterministic solution of the field equations
the expansion θ in the model is considered as proportional to the eigen value s2 2\sigma^{2}_{~2} of the shear tensor sj i\sigma^{j}_{~i} and also the fluid obeys the barotropic equation of state. The vacuum energy density Λ is found to be positive and a decreasing
function of time which is supported by the results from recent supernovae Ia observations. It is also observed that in early
stage of the evolution of the universe string dominates over the particle whereas the universe is dominated by massive string
at the late time. Some physical and geometric properties of the model are also discussed. 相似文献
14.
Ngangbam Ishwarchandra N. Ibohal K. Yugindro Singh 《Astrophysics and Space Science》2014,353(2):633-639
In this paper we present an exact solution of Einstein’s field equations describing the Schwarzschild black hole in dark energy background. It is also regarded as an embedded solution that the Schwarzschild black hole is embedded into the dark energy space producing Schwarzschild-dark energy black hole. It is found that the space-time geometry of Schwarzschild-dark energy solution is non-vacuum Petrov type D in the classification of space-times. We study the energy conditions (like weak, strong and dominant conditions) for the energy-momentum tensor of the Schwarzschild-dark energy solution. We also find that the energy-momentum tensor of the Schwarzschild-dark energy solution violates the strong energy condition due to the negative pressure leading to a repulsive gravitational force of the matter field in the space-time. It is shown that the time-like vector field for an observer in the Schwarzschild-dark energy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity and the area of the horizons for the Schwarzschild-dark energy black hole. 相似文献
15.
We study the Brans-Dicke vacuum field equations in the presence of a cosmological term A. Considering a Friedmann-Robertson-Walker metric with flat spatial sections (k=0), we provide a qualitative analysis of the solutions and investigate its asymptotic properties. The general solution of the field equations for arbitrary values ofw and A is obtained.Work supported by CNPq (Brazil). 相似文献
16.
We study a black hole in an expanding Universe during the radiation-dominated stage. In particular, such a black hole may be of the primordial origin. In the case when the black hole radius is much smaller than the cosmological horizon, we found a self-consistent solution for the metric and the matter distribution and its velocity far from the black hole. At distances much smaller than the cosmological horizon our solution coincides with the previously obtained solution for quasi-stationary accretion. Our results can be applied, in particular, for the formation of dark matter density spikes around primordial black holes, and for the evolution of dark matter clumps during the radiation-dominated stage. 相似文献
17.
Antonio Alfonso-Faus 《Astrophysics and Space Science》2008,318(1-2):117-123
In 1937 Dirac proposed the large number hypothesis (LNH). The idea was to explain that these numbers were large because the Universe is old. A time variation of certain “constants” was assumed. So far, no experimental evidence has significantly supported this time variation. Here we present a simplified cosmological model. We propose a new cosmological system of units, including a cosmological Planck’s constant that “absorbs” the well known large number 10120. With this new Planck’s constant no large numbers appear at the cosmological level. They appear at lower levels, e.g. at the quantum world. We note here that Zel’dovich formula, for the cosmological constant Λ, is equivalent to the Weinberg’s relation. The immediate conclusion is that the speed of light c must be proportional to the Hubble parameter H, and therefore decrease with time. We find that the gravitational radius of the Universe and its size are one and the same constant (Mach’s principle). The usual cosmological Ω’s parameters for mass, lambda and curvature turn out to be all constants of order one. The anthropic principle is not necessary in this theory. It is shown that a factor of 1061 converts in this theory a Planck fluctuation (a quantum black hole) into a cosmological quantum black hole: the Universe today. General relativity and quantum mechanics give the same local solution of an expanding Universe with the law a(t)≈const?t. This constant is just the speed of light today. Then the Hubble parameter is exactly H=a(t)′/a(t)=1/t. 相似文献
18.
We present an exact solution of the vacuum Brans-Dicke field equations for cosmological models of Bianchi type-VI0. The solution represents anisotropic universe which has no analogy in Einstein's theory. 相似文献
19.
《New Astronomy》2021
This paper explores the collapsing process of a unidirectional isotropic matter configuration. The junction conditions for a static exterior geometry and the non-static interior geometry are expressed in terms of the cosmological constant. The time-lapse for the appearance of the black hole and the cosmological horizon is calculated. It is observed that in the de-Sitter space, the unidirectional perfect fluid flow does not make the collapse disappear. The vacuum energy of the cosmological constant makes the collapsing process quite slow and affects the time-lapse of horizon formation. Moreover, the presence of string tension increases the time-lapse of horizon formation. 相似文献
20.
Using the quantum statistical method, we calculate quantum statistical entropy between the black hole horizon and the cosmological horizon in Schwarzchild spacetime and derive the expression of quantum statistical entropy in de Sitter spacetime. Under the Unruh-Verlinde temperature of Schwarzchild-de Sitter spacetime in the entropic force views, we obtain the expression of quantum statistical entropy in de Sitter spacetime. It is shown that in de Sitter spacetime quantum statistical entropy is the sum of thermodynamic entropy corresponding black hole horizon and the one corresponding cosmological horizon. And the correction term of de Sitter spacetime entropy is obtained. Therefore, it is confirmed that the black hole entropy is the entropy of quantum field outside the black hole horizon. The entropy of de Sitter spacetime is the entropy of quantum field between the black hole horizon and the cosmological horizon. 相似文献