154 research outputs found
Scalar models for the unification of the dark sector
We review the difficulties of the generalized Chaplygin gas model to fit
observational data, due to the tension between background and perturbative
tests. We argue that such issues may be circumvented by means of a
self-interacting scalar field representation of the model. However, this
proposal seems to be successful only if the self-interacting scalar field has a
non-canonical form. The latter can be implemented in Rastall's theory of
gravity.Comment: Latex file, 8 pages, 3 figures in eps format. To appear in the
proceedings of the CosmoSul conference, held in Rio de Janeiro, Brazil, 01-05
august of 201
Late time cosmological approach in mimetic gravity
In this paper, we investigate the late-time cosmic acceleration in mimetic
gravity with Lagrange multiplier and potential in a Universe
containing, besides radiation and dark energy, a self-interacting (collisional)
matter. We obtain through the modified Friedmann equations, the main equation
that can describe the cosmological evolution and with several models from
and the well known particular model , we perform an analysis of
the late-time evolution. We examine the behavior of the Hubble parameter, the
dark energy equation of state and the total effective equation of state and we
compare in each case the resulting picture with the non-collisional matter
(assumed as dust) and also with the collisional matter in mimetic
gravity. The results obtained are in good agreement with the observational data
and show that in presence of the collisional matter the dark energy
oscillations in mimetic f(R, T) gravity can be damped.Comment: 18 pages, 2 figure
Late time cosmological approach in mimetic gravity
In this paper, we investigate the late-time cosmic acceleration in mimetic
gravity with Lagrange multiplier and potential in a Universe
containing, besides radiation and dark energy, a self-interacting (collisional)
matter. We obtain through the modified Friedmann equations, the main equation
that can describe the cosmological evolution and with several models from
and the well known particular model , we perform an analysis of
the late-time evolution. We examine the behavior of the Hubble parameter, the
dark energy equation of state and the total effective equation of state and we
compare in each case the resulting picture with the non-collisional matter
(assumed as dust) and also with the collisional matter in mimetic
gravity. The results obtained are in good agreement with the observational data
and show that in presence of the collisional matter the dark energy
oscillations in mimetic f(R, T) gravity can be damped.Comment: 18 pages, 2 figure
Rastall Cosmology and the \Lambda CDM Model
Rastall's theory is based on the non-conservation of the energy-momentum
tensor. We show that, in this theory, if we introduce a two-fluid model, one
component representing vacuum energy whereas the other pressureless matter
(e.g. baryons plus cold dark matter), the cosmological scenario is the same as
for the \Lambda CDM model, both at background and linear perturbative levels,
except for one aspect: now dark energy may cluster. We speculate that this can
lead to a possibility of distinguishing the models at the non-linear
perturbative level.Comment: 9 pages, 1 figure. Accepted for publication in Physical Review
The Brans-Dicke-Rastall theory
We formulate a theory combining the principles of a scalar-tensor gravity and
Rastall's proposal of a violation of the usual conservation laws. We obtain a
scalar-tensor theory with two parameters and , the latter
quantifying the violation of the usual conservation laws. The only exact
spherically symmetric solution is that of Robinson-Bertotti besides
Schwarzschild solution. A PPN analysis reveals that General Relativity results
are reproduced when . The cosmological case displays a possibility
of deceleration/acceleration or acceleration/deceleration transitions during
the matter dominated phase depending on the values of the free parameters.Comment: 17 pages, 3 figure
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