96 research outputs found
Cosmic infinity: a dynamical system approach
Dynamical system techniques are extremely useful to study cosmology. It turns
out that in most of the cases, we deal with finite isolated fixed points corresponding to a given
cosmological epoch. However, it is equally important to analyse the asymptotic behaviour
of the universe. On this paper, we show how this can be carried out for 3-forms model.
In fact, we show that there are fixed points at infinity mainly by introducing appropriate
compactifications and defining a new time variable that washes away any potential divergence
of the system. The richness of 3-form models allows us as well to identify normally hyperbolic
non-isolated fixed points. We apply this analysis to three physically interesting situations:
(i) a pre-inflationary era; (ii) an inflationary era; (iii) the late-time dark matter/dark energy
epoch.The work of MBL is supported by the Portuguese Agency Fundação para a Ciência e Tecnologia through an Investigador FCT Research contract, with refer- ence IF/01442/2013/ CP1196/CT0001. MBL and JMorais wish to acknowledge the sup- port from the Basque government Grant No. IT592-13 (Spain), FONDOS FEDER under grant FIS2014-57956-P (Spanish government) and the COST Action CA15117 (CANTATA). JMorais is also thankful to UPV/EHU for a PhD fellowship. This research work is supported by the grant UID/MAT/00212/2013.info:eu-repo/semantics/publishedVersio
Quantum behavior of FRW radiation-filled universes
We study the quantum vacuum fluctuations around closed Friedmann-Robertson-Walker (FRW) radiation-filled universes with a nonvanishing cosmological constant. These vacuum fluctuations are represented by a conformally coupled massive scalar field and are treated in the lowest order of perturbation theory. In the semiclassical approximation, the perturbations are governed by differential equations which, properly linearized, become generalized Lame equations. The wave function thus obtained must satisfy appropriate regularity conditions which ensure its finiteness for every field configuration. We apply these results to asymptotically anti-de Sitter Euclidean wormhole spacetimes and show that there is no catastrophic particle creation in the Euclidean region, which would lead to divergences of the wave function
False vacuum decay in a brane world cosmological model
The false vacuum decay in a brane world model is studied in this work. We
investigate the vacuum decay via the Coleman-de Luccia instanton, derive
explicit approximative expressions for the Coleman-de Luccia instanton which is
close to a Hawking-Moss instanton and compare the results with those already
obtained within Einstein's theory of relativity.Comment: minor changes done, references added, version to appear in GR
Statefinder parameters for quintom dark energy model
We perform in this paper a statefinder diagnostic to a dark energy model with
two scalar fields, called "quintom", where one of the scalar fields has a
canonical kinetic energy term and the other has a negative one. Several kinds
of potentials are discussed. Our results show that the statefinder diagnostic
can differentiate quintom model with other dark energy models.Comment: 11 pages, including 8 figures, added reference
Cosmological braneworld solutions with bulk scalar field in DGP setup
We study cosmological dynamics of a canonical bulk scalar field in the DGP
setup within a superpotential approach. We show that the normal branch of this
DGP-inspired model realizes a late-time de Sitter expansion on the brane. We
extend this study to the case that the bulk contains a phantom scalar field.
Our detailed study in the supergravity-style analysis reveals some yet
unexplored aspects of cosmological dynamics of bulk scalar field in the normal
DGP setup. Some clarifying examples along with numerical analysis of the model
parameter space are presented in each case.Comment: 29 pages, 12 figs, accepted for publication in Astroparticle Physic
Non linear equation of state and effective phantom divide in brane models
Here, DGP model of brane-gravity is analyzed and compared with the standard
general relativity and Randall-Sundrum cases using non-linear equation of
state. Phantom fluid is known to violate the weak energy condition. In this
paper, it is found that this characteristic of phantom energy is affected
drastically by the negative brane-tension of the RS-II model. It is
found that in DGP model strong energy condition(SEC) is always violated and the
universe accelerates only where as in RS-II model even SEC is not violated for
and the universe decelerates
Astronomical bounds on future big freeze singularity
Recently it was found that dark energy in the form of phantom generalized
Chaplygin gas may lead to a new form of the cosmic doomsday, the big freeze
singularity. Like the big rip singularity, the big freeze singularity would
also take place at a finite future cosmic time, but unlike the big rip
singularity it happens for a finite scale factor.Our goal is to test if a
universe filled with phantom generalized Chaplygin gas can conform to the data
of astronomical observations. We shall see that if the universe is only filled
with generalized phantom Chaplygin gas with equation of state
with , then such a model cannot be matched
to the data of astronomical observations. To construct matched models one
actually need to add dark matter. This procedure results in cosmological
scenarios which do not contradict the data of astronomical observations and
allows one to estimate how long we are now from the future big freeze doomsday.Comment: 8 page
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