13,712 research outputs found
The growth of matter perturbations in f(R) models
We consider the linear growth of matter perturbations on low redshifts in
some dark energy (DE) models. We discuss the definition of dark energy
(DE) in these models and show the differences with scalar-tensor DE models. For
the model recently proposed by Starobinsky we show that the growth
parameter takes the value for
and for , allowing
for a clear distinction from CDM. Though a scale-dependence appears in
the growth of perturbations on higher redshifts, we find no dispersion for
on low redshifts up to , is also
quasi-linear in this interval. At redshift , the dispersion is still
small with . As for some scalar-tensor models, we
find here too a large value for ,
for and for
. These values are largely outside the range found for DE
models in General Relativity (GR). This clear signature provides a powerful
constraint on these models.Comment: 14 pages, 7 figures, improved presentation, references added, results
unchanged, final version to be published in JCA
Design used as a resource In the Increase in the value of goods and cultures: project design and competitive integration in the estrada real territory, Brazil (phase II)
Building analytical three-field cosmological models
A difficult task to deal with is the analytical treatment of models composed
by three real scalar fields, once their equations of motion are in general
coupled and hard to be integrated. In order to overcome this problem we
introduce a methodology to construct three-field models based on the so-called
"extension method". The fundamental idea of the procedure is to combine three
one-field systems in a non-trivial way, to construct an effective three scalar
field model. An interesting scenario where the method can be implemented is
within inflationary models, where the Einstein-Hilbert Lagrangian is coupled
with the scalar field Lagrangian. We exemplify how a new model constructed from
our method can lead to non-trivial behaviors for cosmological parameters.Comment: 11 pages, and 3 figures, updated version published in EPJ
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