126 research outputs found
Einstein static Universe in non-minimal kinetic coupled gravity
We study the stability of Einstein static Universe, with FLRW metric, by
considering linear homogeneous perturbations in the kinetic coupled gravity. By
taking linear homogeneous perturbations, we find that the stability of Einstein
static Universe, in the kinetic coupled gravity with quadratic scalar field
potential, for closed () isotropic and homogeneous FLRW Universe depends
on the coupling parameters and . Specifically, for
and we find that the stability condition imposes
the inequality on the initial size of the closed
Einstein static Universe before the inflation. Such inequality asserts that the
initial size of the Einstein static Universe must be greater than the Planck
length , in consistency with the quantum gravity and quantum cosmology
requirements. In this way, we have determined the non-minimal coupling
parameter in the context of Einstein static Universe. Such a very
small parameter is favored in the inflationary models constructed in the
kinetic coupled gravity. We have also studied the stability against the vector
and tensor perturbations and discussed on the acceptable values of the equation
of state parameter.Comment: 7 page
Vacuum spherically symmetric solutions in gravity
Spherically symmetric static vacuum solutions have been built in
models of gravity theory. We apply some conditions on the metric components;
then the new vacuum spherically symmetric solutions are obtained. Also, by
extracting metric coefficients we determine the analytical form of .Comment: 8 pages,typos corrected, Refs. adde
Einstein Static Universe in Braneworld Scenario
The stability of Einstein static universe against homogeneous scalar
perturbations in the context of braneworld scenario is investigated. The
stability regions are obtained in terms of the constant geometric linear
equation of state parameter and are
studied for each evolutionary era of the universe. The results are discussed
for the case of closed, open or flat universe in each era under the obtained
restricting conditions. We also briefly investigate the stability against
vector and tensor perturbations. Contrary to the classical general relativity,
it is found that a stable Einstein static universe may exist in a braneworld
theory of gravity against scalar, vector and tensor perturbations for some
suitable values and ranges of the cosmological parameters.Comment: 6 pages, one section added, accepted in PLB. arXiv admin note: text
overlap with arXiv:1202.1397 by other author
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