共查询到20条相似文献,搜索用时 15 毫秒
1.
We study effects of cosmic fluids on finite-time future singularities in modified f (R, G)-gravity, where R and G are the Ricci scalar and the Gauss–Bonnet invariant, respectively. We consider the fluid equation of state in the general
form, ω = ω(ρ), and we suppose the existence of a bulk viscosity. We investigate quintessence region (ω > −1) and phantom region (ω < −1) and the possibility to change or avoid the singularities in f (R, G)-gravity. Finally, we study the inclusion of quantum effects in large curvature regime. 相似文献
2.
3.
4.
A new class of solutions which yields an (n + 1)-dimensional spacetime with a longitudinal nonlinear magnetic field is introduced. These spacetimes have no curvature
singularity and no horizon, and the magnetic field is non singular in the whole spacetime. They may be interpreted as traversable
wormholes which could be supported by matter not violating the weak energy conditions. We generalize this class of solutions
to the case of rotating solutions and show that the rotating wormhole solutions have a net electric charge which is proportional
to the magnitude of the rotation parameter, while the static wormhole has no net electric charge. Finally, we use the counterterm
method and compute the conserved quantities of these spacetimes. 相似文献
5.
Guido Cognola Emilio Elizalde Shin’ichi Nojiri Sergei D. Odintsov Sergio Zerbini 《The European Physical Journal C - Particles and Fields》2009,64(3):483-494
We discuss the classical and quantum properties of non-local modified Gauss–Bonnet gravity in de Sitter space, using its equivalent
representation via string-inspired local scalar-Gauss–Bonnet gravity with a scalar potential. A classical, multiple de Sitter
universe solution is found where one of the de Sitter phases corresponds to the primordial inflationary epoch, while the other
de Sitter space solution—the one with the smallest Hubble rate—describes the late-time acceleration of our universe. A Chameleon
scenario for the theory under investigation is developed, and it is successfully used to show that the theory complies with
gravitational tests. An explicit expression for the one-loop effective action for this non-local modified Gauss–Bonnet gravity
in the de Sitter space is obtained. It is argued that this effective action might be an important step towards the solution
of the cosmological constant problem. 相似文献
6.
We construct generalizations of the D=5 Kerr black string by including higher curvature corrections to the gravity action in the form of the Gauss–Bonnet density. These uniform black strings satisfy a generalized Smarr relation and share the basic properties of the Einstein gravity solutions. However, they exist only up to a maximal value of the Gauss–Bonnet coupling constant, which depends on the solutions? mass and angular momentum. 相似文献
7.
The conditions for the existence and stability of cosmological power-law scaling solutions are established when the Einstein–Hilbert
action is modified by the inclusion of a function of the Gauss–Bonnet curvature invariant. The general form of the action
that leads to such solutions is determined for the case where the universe is sourced by a barotropic perfect fluid. It is
shown by employing an equivalence between the Gauss–Bonnet action and a scalar–tensor theory of gravity that the cosmological
field equations can be written as a plane autonomous system. It is found that stable scaling solutions exist when the parameters
of the model take appropriate values. 相似文献
8.
Abhik Kumar Sanyal Claudio Rubano Ester Piedipalumbo 《General Relativity and Gravitation》2011,43(10):2807-2820
Noether symmetry for Gauss–Bonnet Dilatonic interaction exists for a constant dilatonic scalar potential and a linear functional
dependence of the coupling parameter on the scalar field. The symmetry with the same form of the potential and coupling parameter
exists all in the vacuum, radiation and matter dominated era. The late time acceleration is driven by the effective cosmological
constant rather than the Gauss–Bonnet term, while the later compensates for the large value of the effective cosmological
constant giving a plausible answer to the well-known coincidence problem. 相似文献
9.
Masao Iihoshi 《General Relativity and Gravitation》2011,43(6):1571-1576
Einstein–Gauss–Bonnet gravity coupled to a dynamical dilaton is examined from the viewpoint of Einstein’s equivalence principle.
We point out that the usual frame change that applies to the action without curvature correction does not cure the problem
of nonminimal couplings by the dynamical nature of a dilaton field. Thus a modification of the Einstein frame is required.
It is proposed that the kinetic term of a dilaton should be brought to a canonical form, which completely fixes the additional
terms associated with the frame transformation. 相似文献
10.
11.
We obtain cosmological solutions which admit emergent universe (EU) scenario in the framework of Einstein Gauss–Bonnet (GB)
gravity coupled with a dilaton field in 4-dimensions. The coupling parameter of the GB terms and the dilaton in the theory
are determined for obtaining an EU scenario. The corresponding dilaton potential which admits such scenario is determined.
It is found that the GB terms coupled with a dilaton field plays an important role in describing the dynamics of the evolution
of the early as well as the late universe. We note an interesting case where the GB term dominates initially in the asymptotic
past regime, subsequently it decreases and thereafter its contribution in determining the dynamics of the evolution dominates
once again. We note that the Einstein’s static universe solution permitted here is unstable which the asymptotic EU might
follow. We also compare our EU model with supernova data. 相似文献
12.
The field equations for static EGBM gravity are obtained and transformed to an equivalent form through a coordinate redefinition. A form for one of the metric potentials that generalizes the spheroidal ansatz of Vaidya–Tikekar superdense stars and additionally prescribing the electric field intensity yields viable solutions. Some special cases of the general solution are considered and analogous classes in the Einstein framework are studied. In particular the Finch–Skea ansatz is examined in detail and found to satisfy the elementary physical requirements. These include positivity of pressure and density, the existence of a pressure free hypersurface marking the boundary, continuity with the exterior metric, a subluminal sound speed as well as the energy conditions. Moreover, the solution possesses no coordinate singularities. It is found that the impact of the Gauss–Bonnet term is to correct undesirable features in the pressure profile and sound speed index when compared to the equivalent Einstein gravity model. Furthermore graphical analyses suggest that higher densities are achievable for the same radial values when compared to the 5-dimensional Einstein case. The case of a constant gravitational potential, isothermal distribution as well as an incompressible fluid are studied. All exact solutions derived exhibit an equation of state explicitly. 相似文献
13.
D. Bazeia R. Menezes A. Y. Petrov 《The European Physical Journal C - Particles and Fields》2008,58(1):171-177
We investigate non-perturbative dilatonic solutions of the wide class of the modified gravity models that include Gauss–Bonnet
terms with a general F(G) Lagrangian. We show that the presence of Liouville-like solutions is a characteristic feature of these models. 相似文献
14.
15.
Maurya S. K. Pradhan Anirudh Tello-Ortiz Francisco Banerjee Ayan Nag Riju 《The European Physical Journal C - Particles and Fields》2021,81(9):1-11
The European Physical Journal C - Baryon inhomogeneities are generated early in the universe. These inhomogeneities affect the phase transition dynamics of subsequent phase transitions, they also... 相似文献
16.
Kazuharu Bamba Sergei D. Odintsov Lorenzo Sebastiani Sergio Zerbini 《The European Physical Journal C - Particles and Fields》2010,67(1-2):295-310
We study all four types of finite-time future singularities emerging in the late-time accelerating (effective quintessence/phantom) era from ?(R,G)-gravity, where R and G are the Ricci scalar and the Gauss–Bonnet invariant, respectively. As an explicit example of ?(R,G)-gravity, we also investigate modified Gauss–Bonnet gravity, so-called F(G)-gravity. In particular, we reconstruct the F(G)-gravity and ?(R,G)-gravity models where accelerating cosmologies realizing the finite-time future singularities emerge. Furthermore, we discuss a possible way to cure the finite-time future singularities in F(G)-gravity and ?(R,G)-gravity by taking into account higher-order curvature corrections. The example of non-singular realistic modified Gauss–Bonnet gravity is presented. It turns out that adding such non-singular modified gravity to singular Dark Energy makes the combined theory a non-singular one as well. 相似文献
17.
In this work, we have investigated the dynamical instability of spherically symmetric gravitating object under expansion-free condition in Einstein Gauss–Bonnet gravity. In this context, the field equations and dynamical equations have been established in the Gauss–Bonnet gravity. The linear perturbation scheme has been used on the dynamical equations to construct the collapse equation. The Newtonian, post Newtonian and post Newtonian approximations have been applied to investigate the general dynamical (in)stability equations. It has been observed that the instability range of the collapsing source is independent of adiabatic index Γ (stiffness of the fluid does not play any role). The instability range can be determined by the pressure anisotropy, energy density profile, Gauss–Bonnet parameter α and some constraints at Newtonian, post Newtonian and post Newtonian order. 相似文献
18.
19.
Metin Gürses 《General Relativity and Gravitation》2008,40(9):1825-1830
We give all exact solutions of the Einstein–Gauss–Bonnet Field Equations coupled with a scalar field in four dimensions under
certain assumptions. The main assumption we make in this work is to take the second covariant derivative of the coupling function
proportional to the spacetime metric tensor. Although this assumption simplifies the field equations considerably, to obtain
exact solutions we assume also that the spacetime metric is conformally flat. Then we obtain a class of exact solutions. 相似文献