20 research outputs found
Deflationary Models Driven by Matter Creation
A nonsingular deflationary cosmology driven by adiabatic matter creation is
proposed. In this scenario there is no preinflationary stage as happens in
conventional inflationary models. Deflation starts from a de Sitter spacetime
characterized by an arbitrary time scale , which also pins down an
initial value for the temperature of the universe. The model evolves
continuously towards a slightly modified Friedman-Robertson-Walker universe.
The horizon and other well known problems of the standard model are then solved
but, unlike in microscopic models of inflation, there is no supercooling and
subsequent reheating. Entropy generation is concomitant with deflation and if
is of the order of the Planck time, the present day value of the
radiation temperature is deduced. It is also shown that the ``age problem''
does not exist here. In particular, the theoretically favored FRW flat model is
old enough to agree with the observations even given the high values of
suggested by recent measurements.Comment: 17 pages, 2 figures(available from the authors), uses LATE
Crossing the phantom divide with Ricci-like holographic dark energy
We study a holographic model for the dark energy considered recently in the
literature which postulates an energy density , where is the
Ricci scalar curvature. We obtain a cosmological scenario that comes from
considering two non-interacting fluids along a reasonable Ansatz for the cosmic
coincidence parameter. We adjust the involved parameters in the model according
to the observational data and we show that the equation of state for the dark
energy experience a cross through the -1 barrier. In addition, we find a
disagreement in these parameters with respect to an approach from a scalar
field theory.Comment: Match with accepted version by EPJ
The Corley-Jacobson dispersion relation and trans-Planckian inflation
In this Letter we study the dependence of the spectrum of fluctuations in
inflationary cosmology on possible effects of trans-Planckian physics, using
the Corley/Jacobson dispersion relations as an example. We compare the methods
used in previous work [1] with the WKB approximation, give a new exact
analytical result, and study the dependence of the spectrum obtained using the
approximate method of Ref. [1] on the choice of the matching time between
different time intervals. We also comment on recent work subsequent to Ref. [1]
on the trans-Planckian problem for inflationary cosmology.Comment: 6 pages, Revtex
CDM Accelerating Cosmology as an Alternative to LCDM model
A new accelerating cosmology driven only by baryons plus cold dark matter
(CDM) is proposed in the framework of general relativity. In this model the
present accelerating stage of the Universe is powered by the negative pressure
describing the gravitationally-induced particle production of cold dark matter
particles. This kind of scenario has only one free parameter and the
differential equation governing the evolution of the scale factor is exactly
the same of the CDM model. For a spatially flat Universe, as predicted
by inflation (), it is found that the
effectively observed matter density parameter is ,
where is the constant parameter specifying the CDM particle creation
rate. The supernovae test based on the Union data (2008) requires so that as independently derived from weak
gravitational lensing, the large scale structure and other complementary
observations.Comment: 6 pages, 3 figure
Topological defects: A problem for cyclic universes?
We study the behaviour of cosmic string networks in contracting universes,
and discuss some of their possible consequences. We note that there is a
fundamental time asymmetry between defect network evolution for an expanding
universe and a contracting universe. A string network with negligible loop
production and small-scale structure will asymptotically behave during the
collapse phase as a radiation fluid. In realistic networks these two effects
are important, making this solution only approximate. We derive new scaling
solutions describing this effect, and test them against high-resolution
numerical simulations. A string network in a contracting universe, together
with the gravitational radiation background it has generated, can significantly
affect the dynamics of the universe both locally and globally. The network can
be an important source of radiation, entropy and inhomogeneity. We discuss the
possible implications of these findings for bouncing and cyclic cosmological
models.Comment: 11 RevTeX 4 pages, 6 figures; version to appear in Phys. Rev.
Holographic dark energy in a non-flat universe with Granda-Oliveros cut-off
Motivated by Granda and Oliveros (GO) model, we generalize their work to the
non-flat case. We obtain the evolution of the dark energy density, the
deceleration and the equation of state parameters for the holographic dark
energy model in a non-flat universe with GO cut-off. In the limiting case of a
flat universe, i.e. , all results given in GO model are obtained.Comment: 11 pages, 5 figure
Cosmological evolution and statefinder diagnostic for new holographic dark energy model in non flat universe
In this paper, the holographic dark energy model with new infrared cut-off
proposed by Granda and Oliveros has been investigated in spatially non flat
universe. The dependency of the evolution of equation of state, deceleration
parameter and cosmological evolution of Hubble parameter on the parameters of
new HDE model are calculated. Also, the statefinder parameters and in
this model are derived and the evolutionary trajectories in plane are
plotted. We show that the evolutionary trajectories are dependent on the model
parameters of new HDE model. Eventually, in the light of SNe+BAO+OHD+CMB
observational data, we plot the evolutionary trajectories in and
planes for best fit values of the parameters of new HDE model.Comment: 11 pages, 5 figures, Accepted by Astrophys. Space Sc