7 research outputs found
Observational hints on the Big Bounce
In this paper we study possible observational consequences of the bouncing
cosmology. We consider a model where a phase of inflation is preceded by a
cosmic bounce. While we consider in this paper only that the bounce is due to
loop quantum gravity, most of the results presented here can be applied for
different bouncing cosmologies. We concentrate on the scenario where the scalar
field, as the result of contraction of the universe, is driven from the bottom
of the potential well. The field is amplified, and finally the phase of the
standard slow-roll inflation is realized. Such an evolution modifies the
standard inflationary spectrum of perturbations by the additional oscillations
and damping on the large scales. We extract the parameters of the model from
the observations of the cosmic microwave background radiation. In particular,
the value of inflaton mass is equal to GeV. In
our considerations we base on the seven years of observations made by the WMAP
satellite. We propose the new observational consistency check for the phase of
slow-roll inflation. We investigate the conditions which have to be fulfilled
to make the observations of the Big Bounce effects possible. We translate them
to the requirements on the parameters of the model and then put the
observational constraints on the model. Based on assumption usually made in
loop quantum cosmology, the Barbero-Immirzi parameter was shown to be
constrained by from the cosmological observations. We have
compared the Big Bounce model with the standard Big Bang scenario and showed
that the present observational data is not informative enough to distinguish
these models.Comment: 25 pages, 8 figures, JHEP3.cl
AIC, BIC, Bayesian evidence against the interacting dark energy model
Recent astronomical observations have indicated that the Universe is in the
phase of accelerated expansion. While there are many cosmological models which
try to explain this phenomenon, we focus on the interacting CDM model
where the interaction between the dark energy and dark matter sectors takes
place. This model is compared to its simpler alternative---the CDM
model. To choose between these models the likelihood ratio test was applied as
well as the model comparison methods (employing Occam's principle): the Akaike
information criterion (AIC), the Bayesian information criterion (BIC) and the
Bayesian evidence. Using the current astronomical data: SNIa (Union2.1),
, BAO, Alcock--Paczynski test and CMB we evaluated both models. The
analyses based on the AIC indicated that there is less support for the
interacting CDM model when compared to the CDM model, while
those based on the BIC indicated that there is the strong evidence against it
in favor the CDM model. Given the weak or almost none support for the
interacting CDM model and bearing in mind Occam's razor we are
inclined to reject this model.Comment: LaTeX svjour3, 12 pages, 3 figure
Future sudden singularities in Palatini cosmology
We show that future singularities which have appeared in the Palatini cosmological models investigated in [1] are of finite size at finite time type [2]
Future sudden singularities in Palatini cosmology
We show that future singularities which have appeared in the Palatini cosmological models investigated in [1] are of finite size at finite time type [2]