31,262 research outputs found
CCDM model from quantum particle creation: constraints on dark matter mass
In this work the results from the quantum process of matter creation have
been used in order to constrain the mass of the dark matter particles in an
accelerated Cold Dark Matter model (Creation Cold Dark Matter, CCDM). In order
to take into account a back reaction effect due to the particle creation
phenomenon, it has been assumed a small deviation for the scale
factor in the matter dominated era of the form .
Based on recent data, the best fit values for the mass of dark matter
created particles and the parameter have been found as
GeV, restricted to a 68.3\% c.l. interval of
() GeV and at
68.3\% c.l. For these best fit values the model correctly recovers a transition
from decelerated to accelerated expansion and admits a positive creation rate
near the present era. Contrary to recent works in CCDM models where the
creation rate was phenomenologically derived, here we have used a quantum
mechanical result for the creation rate of real massive scalar particles, given
a self consistent justification for the physical process. This method also
indicates a possible solution to the so called "dark degeneracy", where one can
not distinguish if it is the quantum vacuum contribution or quantum particle
creation which accelerates the Universe expansion.Comment: 16 pages, 5 figures. Major modifications have been done, following
the referee suggestions. The deduction of the treatment is now more
transparent, figures have been added showing the statistical limits over the
dark matter mass, and the best fit for DM mass has been slightly modifie
Particle creation in a f(R) theory with cosmological constraints
In this paper we study the creation of super-massive real scalar particles in
the framework of a modified gravity theory, with parameters
constrained by observational data. The analysis is restrict to a homogeneous
and isotropic flat and radiation dominated universe. We compare the results to
the standard Einstein gravity with cosmological constant ( model),
and we show that the total number density of created particles in the
model is very close to the standard case. Another interesting result is that
the spectrum of created particles is independent at early times.Comment: To appear in the General Relativity and Gravitation. arXiv admin
note: text overlap with arXiv:1108.334
A new approach on the stability analysis in ELKO cosmology
In this work it has been developed a new approach to study the stability of a
system composed by an ELKO field interacting with dark matter, which could give
some contribution in order to alleviate the cosmic coincidence problem. It is
assumed that the potential which characterizes the ELKO field is not specified,
but it is related to a constant parameter . The strength of the
interaction between matter and ELKO field is characterized by a constant
parameter and it is also assumed that both ELKO field as matter energy
density are related to their pressures by equations of state parameters
and , respectively. The system of equations is analysed
by a dynamical system approach. It has been found the conditions of stability
between the parameters and in order to have stable fixed
points for the system for different values of the equation of state parameters
and , and the results are presented in form of tables.
The possibility of decay of ELKO field into dark matter or vice versa can be
read directly from the tables, since the parameters and
satisfy some inequalities. It allows us to constrain the potential assuming
that we have a stable system for different interactions terms between the ELKO
field and dark matter. The cosmic coincidence problem can be alleviated for
some specific relations between the parameters of the model.Comment: 16 pages, some new comments in the Introduction and at the begining
of Section I
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