375 research outputs found
f(R) brane cosmology
Despite the nice features of the Dvali, Gabadadze and Porrati (DGP) model to
explain the late-time acceleration of the universe, it suffers from some
theoretical problems like the ghost issue. We present a way to self-accelerate
the normal DGP branch, which is known to be free of the ghost problem, by means
of an f(R) term on the brane action. We obtain the de Sitter self-accelerating
solutions of the model and study their stability under homogeneous
perturbations.Comment: 4 pages, 2 figures. Contribution to the proceedings of Spanish
Relativity Meeting 2009, Bilbao, Spain, 7-11 September 200
On the thermal boundary condition of the wave function of the Universe
We broaden the domain of application of the recently proposed thermal
boundary condition of the wave function of the Universe, which has been
suggested as the basis of a dynamical selection principle on the landscape of
string solutions.Comment: 3 pages, 3 figures, contribution to the proceedings of MG11, 23-29
July 2006, Berlin, German
Resolution of type IV singularities in quantum cosmology
We discuss the fate of classical type IV singularities in quantum cosmology.
The framework is Wheeler-DeWitt quantization applied to homogeneous and
isotropic universes with a perfect fluid described by a generalized Chaplygin
gas. Such a fluid can be dynamically realized by a scalar field. We treat the
cases of a standard scalar field with positive kinetic energy and of a scalar
field with negative energy (phantom field). We first present the classical
solutions. We then discuss in detail the Wheeler-DeWitt equation for these
models. We are able to give analytic solutions for a special case and to draw
conclusions for the general case. Adopting the criterion that singularities are
avoided if the wave function vanishes in the region of the classical
singularity, we find that type IV singularities are avoided only for particular
solutions of the Wheeler-DeWitt equation. We compare this result with earlier
results found for other types of singularities.Comment: 10 pages, 4 figures, clarifications include
Observational constraints on Chaplygin cosmology in a braneworld scenario with induced gravity and curvature effect
We study cosmological dynamics and late-time evolution of an extended induced
gravity braneworld scenario. In this scenario, curvature effects are taken into
account via the Gauss-Bonnet term in the bulk action and there is also a
Chaplygin gas component on the brane. We show that this model mimics an
effective phantom behavior in a relatively wider range of redshifts than
previously formulated models. It also provides a natural framework for smooth
crossing of the phantom-divide line due to presence of the Chaplygin gas
component on the brane. We confront the model with observational data from type
Ia Supernovae, Cosmic Microwave Background and Baryon Acoustic Oscillations to
constraint the model parameters space.Comment: 19 pages, 11 figures, Accepted for publication in MNRA
The spectrum of gravitational waves in an f(R) model with a bounce
We present an inflationary model preceded by a bounce in a metric
theory. In this model, modified gravity affects only the early stages of the
universe. We analyse the predicted spectrum of the gravitational waves in this
scenario using the method of the Bogoliubov coefficients. We show that there
are distinctive (oscillatory) signals on the spectrum for very low frequencies;
i.e., corresponding to modes that are currently entering the horizon.Comment: 4 pages, 2 figures. Contribution to the Spanish Relativity Meeting in
Portugal 2012 (ERE2012), Guimaraes, Portuga
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