1,114 research outputs found
Teleparallel Minkowski Spacetime with Perturbative Approach for Teleparallel Gravity on Proper Frame
In this paper, we first develop a complete perturbation theory requiring only
the perturbation of the fundamental quantities describing Teleparallel Gravity.
We first obtain the physical quantities by perturbing the coframes taking into
account the gauge metric and spin-connection conditions. We obtain the
perturbed field equations involving these perturbed quantities. We will study
some specific cases of perturbations of coframes and finally discuss the
stability of the Minkowski background. Our perturbation framework is based on
using a proper orthonormal frame throughout, which is possible since we remain
with a theory of Teleparallel Gravity.Comment: 33 pages, submitted to a journa
Brane-world Cosmologies with non-local bulk effects
It is very common to ignore the non-local bulk effects in the study of
brane-world cosmologies using the brane-world approach. However, we shall
illustrate through the use of three different scenarios, that the non-local
bulk-effect does indeed have significant impact on both the
initial and future behaviour of brane-world cosmologies.Comment: 17 pages, no figures, iopart.cls, submitted to CQ
Scalar Field Cosmologies with Barotropic Matter: Models of Bianchi class B
We investigate in detail the qualitative behaviour of the class of Bianchi
type B spatially homogeneous cosmological models in which the matter content is
composed of two non-interacting components; the first component is described by
a barotropic fluid having a gamma-law equation of state, whilst the second is a
non-interacting scalar field (phi) with an exponential potential V=Lambda exp(k
phi). In particular, we study the asymptotic properties of the models both at
early and late times, paying particular attention on whether the models
isotropize (and inflate) to the future, and we discuss the genericity of the
cosmological scaling solutions.Comment: 18 pages, 1 figure, uses revtex and epsf to insert figur
Bianchi Type Cosmological Models in Tele-parallel Gravity
Symmetry assumptions on the geometrical framework have provided successful
mechanisms to develop physically meaningful solutions to many problems. In
tele-parallel gravity, invariance of the frame and spin-connection under a
group of motions defines an affine symmetry group. Here, we assume there exists
a three-dimensional group of affine symmetries acting simply transitively on a
spatial hypersurface and that this group of symmetry actions defines our affine
frame symmetry group. We determine the general form of the co-frame and spin
connection for each spatially homogeneous Bianchi type. We then construct the
corresponding field equations for tele-parallel gravity. We show that if
the symmetry group is of Bianchi type A (, , , , or
) then there exists a co-frame/spin connection pair that is consistent with
the antisymmetric part of the field equations of tele-parallel gravity.
For those geometries having a Bianchi type B symmetry group (, , ,
), we find that in general these geometries are inconsistent with the
antisymmetric part of the tele-parallel gravity field equations unless
the theory reduces to an analog of General Relativity with a cosmological
constant.Comment: 28 page
Dynamics of Generalized Assisted Inflation
We study the dynamics of multiple scalar fields and a barotropic fluid in an
FLRW-universe. The scalar potential is a sum of exponentials. All critical
points are constructed and these include scaling and de Sitter solutions. A
stability analysis of the critical points is performed for generalized assisted
inflation, which is an extension of assisted inflation where the fields
mutually interact. Effects in generalized assisted inflation which differ from
assisted inflation are emphasized. One such a difference is that an
(inflationary) attractor can exist if some of the exponential terms in the
potential are negative.Comment: 27 page
Modulation of Multiple Sclerosis and its Animal Model experimental Autoimmune encephalomyelitis by Food and Gut Microbiota
Multiple sclerosis (MS) is an autoimmune neurological disease characterized by chronic inflammation of the central nervous system (CNS), leading to demyelination, axonal damage, and symptoms such as fatigue and disability. Although the cause of MS is not known, the infiltration of peripherally activated immune cells into the CNS has a key pathogenic role. Accumulating evidence supports an important role of diet and gut microbiota in immune-mediated diseases. Preclinical as well as clinical studies suggest a role for gut microbiota and dietary components in MS. Here, we review these recent studies on gut microbiota and dietary interventions in MS and its animal model experimental autoimmune encephalomyelitis. We also propose directions for future research
- …