1,244 research outputs found
Gauss-Bonnet dark energy by Lagrange multipliers
A string-inspired effective theory of gravity, containing Gauss-Bonnet
invariant interacting with a scalar field, is considered in view of obtaining
cosmological dark energy solutions. A Lagrange multiplier is inserted into the
action in order to achieve the cosmological reconstruction by selecting
suitable forms of couplings and potentials. Several cosmological exact
solutions (including dark energy of quintessence, phantom or Little Rip type)
are derived in presence and in absence of the Lagrange multiplier showing the
difference in the two dynamical approaches. In the models that we consider, the
Lagrange multiplier behaves as a sort of dust fluid that realizes the
transitions between matter dominated and dark energy epochs. The relation
between Lagrange multipliers and Noether symmetries is discussed.Comment: 14 pages, expanded version to appear in PR
Little Rip, CDM and singular dark energy cosmology from Born-Infeld- gravity
We study late-time cosmic accelerating dynamics from Born-Infeld-
gravity in a simplified conformal approach. We find that a variety of cosmic
efects such as Little Rip, CDM universe and dark energy cosmology with
finite-time future singularities may occur. Unlike the convenient Born-Infeld
gravity where in the absence of matter only de Sitter expansion may emerge,
apparentlly any FRW cosmology maybe reconstructed from this conformal version
of the Born-Infeld- theory. Despite the fact that the explicit form of
is fixed by the conformal ansatz, the relation between the two metrics
in this approach may be changed so as to bring out any desired FRW cosmology.Comment: 7 pages, 5 figures. This version accepted in Phys. Lett.
Higher-Order Gauss-Bonnet Cosmology
We study cosmological models derived from higher-order Gauss-Bonnet gravity
by using the Lagrange multiplier approach without assuming the
presence of additional fields with the exception of standard perfect fluid
matter. The presence of Lagrange multipliers reduces the number of allowed
solutions. We need to introduce compatibility conditions of the FRW equations,
which impose strict restrictions on the metric or require the introduction of
additional exotic matter. Several classes of models are generated and
discussed.Comment: 8 pages, to appear in Astro. Space Sc
Bounce universe from string-inspired Gauss-Bonnet gravity
We explore cosmology with a bounce in Gauss-Bonnet gravity where the
Gauss-Bonnet invariant couples to a dynamical scalar field. In particular, the
potential and and Gauss-Bonnet coupling function of the scalar field are
reconstructed so that the cosmological bounce can be realized in the case that
the scale factor has hyperbolic and exponential forms. Furthermore, we examine
the relation between the bounce in the string (Jordan) and Einstein frames by
using the conformal transformation between these conformal frames. It is shown
that in general, the property of the bounce point in the string frame changes
after the frame is moved to the Einstein frame. Moreover, it is found that at
the point in the Einstein frame corresponding to the point of the cosmological
bounce in the string frame, the second derivative of the scale factor has an
extreme value. In addition, it is demonstrated that at the time of the
cosmological bounce in the Einstein frame, there is the Gauss-Bonnet coupling
function of the scalar field, although it does not exist in the string frame.Comment: 33 pages, 9 figures, version accepted for publication in JCA
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