27 research outputs found
Stability analysis for cosmological models in gravity using dynamical system analysis
Modified gravity theories have received increased attention lately to
understand the late time acceleration of the universe. This viewpoint
essentially modifies the geometric components of the universe. Among numerous
extension to Einstein's theory of gravity, theories which include higher order
curvature invariant, and specifically the class of theories, have
received several acknowledgments. In our current work we try to understand the
late time acceleration of the universe by modifying the geometry of the space
and using dynamical system analysis. The use of this technique allows to
understand the behavior of the universe under several circumstances. Apart from
that we study the stability properties of the critical point and acceleration
phase of the universe which could then be analyzed with observational data. We
consider a particular model with for the study. As a first case we consider the matter and
radiation component of the universe with an assumption of no interaction
between them. Later, as a second case we take matter, radiation and dark energy
(cosmological constant) where study on effects of linear, non-linear and no
interaction between matter and dark energy is considered and results have been
discussed in detail.Comment: 16 pages and 10 figures, published in EPJ
Dark energy in spherically symmetric universe coupled with Brans-Dicke scalar field
The phenomenon of dark energy and its manifestations are studied in a
spherically symmetric universe considering the Brans-Dicke scalar tensor
theory. In the first model the dark energy behaves like a phantom type and in
such a universe the existence of negative time is validated with an indication
that our universe started its evolution before . Dark energy prevalent in
this universe is found to be more active at times when other types of energies
remain passive. The second model universe begins with big bang. On the other
hand the dark energy prevalent in the third model is found to be of the
quintessence type. Here it is seen that the dark energy triggers the big bang
and after that much of the dark energy reduces to dark matter. One peculiarity
in such a model is that the scalar field is prevalent eternally, it never tends
to zero.Comment: 15 page
Qualitative behavior of cosmological models combining various matter fields
The late time accelerated expansion of the universe can be realized using
scalar fields with given self-interacting potentials. Here we consider a
straightforward approach where a three cosmic fluid mixture is assumed. The
fluids are standard matter perfect fluid, dark matter, and a scalar field with
the role of dark energy. A dynamical system analysis is developed in this
context. A central role is played by the equation of state which
determines the acceleration phase of the models. Determining the domination of
a particular fluid at certain stages of the universe history by stability
analysis allows, in principle, to establish the succession of the various
cosmological eras.Comment: 18 pages, 7 figures, accepted in IJMP