3 research outputs found
Asymptotic analysis of spatially inhomogeneous stiff and ultra-stiff cosmologies
We calculate analytically the past asymptotic decay rates close to an initial
singularity in general G_0 spatially inhomogeneous perfect fluid models with an
effective equation of state which is stiff or ultra-stiff (i.e., ). These results are then supported by numerical simulations in a special
class of G_2 cosmological models. Our analysis confirms and extends the BKL
conjectures and lends support to recent isotropization results in cosmological
models of current interest (with ).Comment: Accepted by CQ
Bulk viscous cosmological model with interacting dark fluids
The objective of the present work is to study a cosmological model for a
spatially flat Universe whose constituents are a dark energy field and a matter
field which includes baryons and dark matter. The constituents are supposed to
be in interaction and irreversible processes are taken into account through the
inclusion of a non-equilibrium pressure. The non-equilibrium pressure is
considered to be proportional to the Hubble parameter within the framework of a
first order thermodynamic theory. The dark energy and matter fields are coupled
by their barotropic indexes, which are considered as functions of the ratio
between their energy densities. The free parameters of the model are adjusted
from the best fits of the Hubble parameter data. A comparison of the viscous
model with the non-viscous one is performed. It is shown that the equality of
the dark energy and matter density parameters and the decelerated-accelerated
transition occur at earlier times when the irreversible processes are present.
Furthermore, the density and deceleration parameters and the distance modulus
have the correct behavior which is expected for a viable scenario of the
present status of the Universe.Comment: 10 pages, 7 figures, to be published in Brazilian Journal of Physic