22 research outputs found
Cosmography in f(T)-gravity
Being based on the only assumption that the universe is homogenous and
isotropic on large scales, cosmography is an ideal tool to investigate the
cosmic expansion history in a almost model-independent way. Fitting the data on
the luminosity distance and Baryon Acoustic Oscillations allows to determine
the confidence ranges for the cosmographic parameters hence giving some
quantitative constraints that a whatever theory has to fulfill. As an
application, we consider here the case of teleparallel gravity (TEGR) also
referred to as f(T)-gravity. To this end, we first work out analytical
expressions to express the present day values of f(T)-derivatives as a function
of the cosmographic parameters which hold under quite general and physically
motivated conditions. We then use the constraints coming from cosmography to
find out the confidence ranges for f(T)-derivatives up to the fifth order and
show how these can be used to check the viability of given TEGR models without
the need to explicitly solve the second order dynamic equations.Comment: 12 pages, 1 figure, to appear in Phys. Rev.
The universe dynamics in the tachyon cosmology with non-minimal coupling to matter
Recently, the tachyon cosmology has been represented as dark energy model to
support the current acceleration of the universe without phantom crossing. In
this paper, we study the dynamics of the tachyon cosmology in which the field
plays the role of tachyon field and also non--minimally coupled to the matter
lagrangian. The model shows current universe acceleration and also phantom
crossing in the future. Two cosmological tests are also performed to validate
the model; the difference in the distance modulus and the model independent
Cosmological Redshift Drift (CRD) test.Comment: 14 pages, 11 figure
On the Dynamics of Bianchi IX cosmological models
A cosmological description of the universe is proposed in the context of
Hamiltonian formulation of a Bianchi IX cosmology minimally coupled to a
massless scalar field. The classical and quantum results are studied with
special attention to the case of closed Friedmann-Robertson-Walker model.Comment: 11 pages, 1 figur
Interacting agegraphic dark energy model in tachyon cosmology coupled to matter
Scalar-field dark energy models for tachyon fields are often regarded as an
effective description of an underlying theory of dark energy. In this paper, we
propose the agegraphic dark energy model in tachyon cosmology by interaction
between the components of the dark sectors. In the formalism, the interaction
term emerges from the tachyon field nonminimally coupled to the matter
Lagrangian in the model rather than being inserted into the formalism as an
external source. The model is constrained by the observational data. Based on
the best fitted parameters in both original and new agegraphic dark energy
scenarios, the model is tested by Sne Ia data. The tachyon potential and
tachyon field are reconstructed and coincidence problem is revisited.Comment: 11 pages, 10 figures. Published in PLB (contains some changes in the
text with respect to the first version); arXiv admin note: text overlap with
arXiv:1106.2659 by same author