62 research outputs found
Cyclic, ekpyrotic and little rip universe in modified gravity
We propose the reconstruction of gravity in such a way that
corresponding theory admits cyclic and ekpyrotic universe solutions. The number
of explicit examples of such model is found. The comparison with the
reconstructed scalar-tensor theory is made. We also present gravity
which provides the little rip evolution and gives the realistic gravitational
alternative for CDM cosmology. The time for little rip dissolution of
bound structures in such theory is estimated. We demonstrate that transformed
little rip solution becomes qualitatively different cosmological
solution with Big Bang type singularity in Einstein frame.Comment: LaTeX 11 pages, no figure, typos correcte
Is exponential gravity a viable description for the whole cosmological history?
Here we analysed a particular type of gravity, the so-called
exponential gravity which includes an exponential function of the Ricci scalar
in the action. Such term represents a correction to the usual Hilbert-Einstein
action. By using Supernovae Ia, Barionic Acoustic Oscillations, Cosmic
Microwave Background and data, the free parameters of the model are well
constrained. The results show that such corrections to General Relativity
become important at cosmological scales and at late-times, providing an
alternative to the dark energy problem. In addition, the fits do not determine
any significant difference statistically with respect to the CDM
model. Finally, such model is extended to include the inflationary epoch in the
same gravitational Lagrangian. As shown in the paper, the additional terms can
reproduce the inflationary epoch and satisfy the constraints from Planck data.Comment: 20 pages, 6 figures, analysis extended, version published in EPJ
Generalized gravity and the late-time cosmic acceleration
High-precision observational data have confirmed with startling evidence that
the Universe is currently undergoing a phase of accelerated expansion. This
phase, one of the most important and challenging current problems in cosmology,
represents a new imbalance in the governing gravitational equations.
Historically, physics has addressed such imbalances by either identifying
sources that were previously unaccounted for, or by altering the gravitational
theory. Several candidates, responsible for this expansion, have been proposed
in the literature, in particular, dark energy models and modified gravity
models, amongst others. Outstanding questions are related to the nature of this
so-called "dark energy" that is driving this acceleration, and whether it is
due to the vacuum energy or a dynamical field. On the other hand, the late-time
cosmic acceleration may be due to modifications of General Relativity. In this
work we explore a generalised modified gravity theory, namely
gravity, where is the Ricci scalar, is a scalar field, and is a
kinetic term. This theory contains a wide range of dark energy and modified
gravity models. We considered specific models and applications to the late-time
cosmic acceleration.Comment: 13 pages, 1 figure; slightly revised version, displayed name
corrected. arXiv admin note: text overlap with arXiv:1412.086
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