1,637 research outputs found
Viable f(R) gravity and future cosmological evolution
One of the so-called viable modified gravities is analyzed. This kind of
gravity theories are characterized by a well behavior at local scales, where
General Relativity is recovered, while the modified terms become important at
the cosmological level, where the late-time accelerating era is reproduced, and
even the inflationary phase. In the present work, the future cosmological
evolution for one of these models is studied. A transition to the phantom phase
is observed. Furthermore, the scalar-tensor equivalence of f(R) gravity is also
considered, which provides important information concerning this kind of
models.Comment: 4 pages. To appear in the proceedings of the Multiverse and
Fundamental Cosmology Conference (Multicosmofun 2012), Szczecin, Polan
Reconstructing cosmological solutions in F(R) gravity. Towards a unified model of the Universe evolution
It is accepted by the majority of scientific community that the Universe is
currently in an accelerated epoch. In order to explain this shock of late 90's,
a lot of dark energy candidates have been proposed. We study in the context of
f (R) gravity, how some modifications on General Relativity could reproduce
such behavior of the cosmic evolution. It is showed that in general, an f (R)
theory can be reconstructed from a non-minimal scalar-tensor theory, where a
desired cosmological solution can be achieved. Some viable models are studied
as well as its cosmological evolution, and the possibility that inflationary
epoch is also a result of these fine modifications.Comment: 4 pages. Contribution to the Proceedings of the Spanish Relativity
Meeting (ERE) 2009, Bilbao, Spai
Cosmological solutions in F(R) Horava-Lifshitz gravity
At the present work, it is studied the extension of F (R) gravities to the
new recently proposed theory of gravity, the so-called Horava-Lifshitz gravity,
which provides a way to make the theory power counting renormalizable by
breaking Lorentz invariance. It is showed that dark energy can be well
explained in the frame of this extension, just in terms of gravity. It is also
explored the possibility to unify inflation and late-time acceleration under
the same mechanism, providing a natural explanation the accelerated expansion.Comment: 4 pages. Contribution to the Proceedings of the Spanish Relativity
Meeting (ERE) 2010, Granada, Spai
Conformal frames and the validity of Birkhoff's theorem
Birkhoff's theorem is one of the most important statements of Einstein's
general relativity, which generally can not be extended to modified theories of
gravity. Here we study the validity of the theorem in scalar-tensor theories
using a perturbative approach, and compare the results in the so-called
Einstein and Jordan frames. The implications of the results question the
physical equivalence between both frames, at least in perturbations.Comment: 4 pages. Contribution to the Proceedings of Spanish Relativity
Meeting ERE2011, Madri
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