22 research outputs found
Thermodynamics of Gravity: The Double Well Potential Case
In this work we further extend the analysis of theories of gravity in
the metric formalism under the approach of a Thermodynamics analogy, proposed
in arXiv:1911.04830v3. Here we assume a double-well inflationary potential in
the Einstein frame and obtain a parametric form of in the corresponding
Jordan frame.
The whole Thermodynamics picture then follows: an equation of state, binodal
and spinodal curves, phase transition, critical quantities (pressure, volume
and temperature), entropy jumps, specific-heat divergence (and the
corresponding critical exponent) and a butterfly catastrophe.Comment: 13 pages, 13 figures. arXiv admin note: substantial text overlap with
arXiv:1911.0483
On Perturbations in Warm Inflation
Warm inflation is an interesting possibility of describing the early
universe, whose basic feature is the absence, at least in principle, of a
preheating or reheating phase. Here we analyze the dynamics of warm inflation
generalizing the usual slow-roll parameters that are useful for characterizing
the inflationary phase. We study the evolution of entropy and adiabatic
perturbations, where the main result is that for a very small amount of
dissipation the entropy perturbations can be neglected and the purely adiabatic
perturbations will be responsible for the primordial spectrum of
inhomogeneities. Taking into account the COBE-DMR data of the cosmic microwave
background anisotropy as well as the fact that the interval of inflation for
which the scales of astrophysical interest cross outside the Hubble radius is
about 50 e-folds before the end of inflation, we could estimate the magnitude
of the dissipation term. It was also possible to show that at the end of
inflation the universe is hot enough to provide a smooth transition to the
radiation era.Comment: 12 pages, no figures, requires revtex4. Further explanation on the
origin of the entropy perturbation, reference added and minor notation
change. Version accepted for publication in Phys. Rev.
Trans-Planckian Physics from a Nonlinear Dispersion Relation
We study a particular nonlinear dispersion relation -- a
series expansion in the physical wavenumber -- for modeling first-order
corrections in the equation of motion of a test scalar field in a de Sitter
spacetime from trans-Planckian physics in cosmology. Using both a numerical
approach and a semianalytical one, we show that the WKB approximation
previously adopted in the literature should be used with caution, since it
holds only when the comoving wavenumber . We determine the amplitude
and behavior of the corrections on the power spectrum for this test field.
Furthermore, we consider also a more realistic model of inflation, the
power-law model, using only a numerical approach to determine the corrections
on the power spectrum.Comment: 11 pages, 10 figures. Some changes made, comments and references
added, a figure added, typos corrected, conclusions unchanged, version
accepted for pubblication in Phys. Rev.
Dark Interactions and Cosmological Fine-Tuning
Cosmological models involving an interaction between dark matter and dark
energy have been proposed in order to solve the so-called coincidence problem.
Different forms of coupling have been studied, but there have been claims that
observational data seem to narrow (some of) them down to something annoyingly
close to the CDM model, thus greatly reducing their ability to deal
with the problem in the first place. The smallness problem of the initial
energy density of dark energy has also been a target of cosmological models in
recent years. Making use of a moderately general coupling scheme, this paper
aims to unite these different approaches and shed some light as to whether this
class of models has any true perspective in suppressing the aforementioned
issues that plague our current understanding of the universe, in a quantitative
and unambiguous way.Comment: 13 pages, 9 figures, accepted for publication in JCAP. Minor
corrections, one figure replaced, references adde
Type Ia supernova parameter estimation: a comparison of two approaches using current datasets
By using the Sloan Digital Sky Survey (SDSS) first year type Ia supernova (SN
Ia) compilation, we compare two different approaches (traditional \chi^2 and
complete likelihood) to determine parameter constraints when the magnitude
dispersion is to be estimated as well. We consider cosmological constant + Cold
Dark Matter (\Lambda CDM) and spatially flat, constant w Dark Energy + Cold
Dark Matter (FwCDM) cosmological models and show that, for current data, there
is a small difference in the best fit values and 30% difference in
confidence contour areas in case the MLCS2k2 light-curve fitter is adopted. For
the SALT2 light-curve fitter the differences are less significant (
13% difference in areas). In both cases the likelihood approach gives more
restrictive constraints. We argue for the importance of using the complete
likelihood instead of the \chi^2 approach when dealing with parameters in the
expression for the variance.Comment: 16 pages, 5 figures. More complete analysis by including peculiar
velocities and correlations among SALT2 parameters. Use of 2D contours
instead of 1D intervals for comparison. There can be now a significant
difference between the approaches, around 30% in contour area for MLCS2k2 and
up to 13% for SALT2. Generic streamlining of text and suppression of section
on model selectio