175 research outputs found
Curvaton Scenario in the Presence of Two Dilatons Coupled to the Scalar Curvature
The possibility of the realization of a curvaton scenario is studied in a
theory in which two dilatons are introduced along with coupling to the scalar
curvature. It is shown that when the two dilatons have an approximate O(2)
symmetric coupling, a scalar field playing the role of the curvaton may exist
in the framework of this theory without introducing any other scalar field for
the curvaton. Thus the curvaton scenario can be realized, and in the simple
version of the curvaton scenario, in which the curvaton potential is quadratic,
the curvature perturbation with a sufficient amplitude and a nearly
scale-invariant spectrum suggested by observations obtained from WMAP can be
generated.Comment: 45 pages, 5 figures, typos correcte
Observational constraints on the jerk parameter with the data of the Hubble parameter
We study the accelerated expansion phase of the universe by using the
{\textit{kinematic approach}}. In particular, the deceleration parameter is
parametrized in a model-independent way. Considering a generalized
parametrization for , we first obtain the jerk parameter (a
dimensionless third time derivative of the scale factor) and then confront it
with cosmic observations. We use the latest observational dataset of the Hubble
parameter consisting of 41 data points in the redshift range of , larger than the redshift range that covered by the Type Ia
supernova. We also acquire the current values of the deceleration parameter
, jerk parameter and transition redshift (at which the
expansion of the universe switches from being decelerated to accelerated) with
errors ( confidence level). As a result, it is demonstrate
that the universe is indeed undergoing an accelerated expansion phase following
the decelerated one. This is consistent with the present observations.
Moreover, we find the departure for the present model from the standard
CDM model according to the evolution of . Furthermore, the
evolution of the normalized Hubble parameter is shown for the present model and
it is compared with the dataset of .Comment: 9 pages, 4 figures, 1 table, new references added, version accepted
for publication in the European Physical Journal
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