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Register a new userMatter Perturbations in Scaling Cosmology
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Added by
W. S. Hipolito-Ricaldi
Publication date
2014
fields
Physics
and research's language is
English
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A suitable nonlinear interaction between dark matter with an energy density $rho_{M}$ and dark energy with an energy density $rho_{X}$ is known to give rise to a non-canonical scaling $rho_{M} propto rho_{X}a^{-xi}$ where $xi$ is a parameter which generally deviates from $xi =3$. Here we present a covariant generalization of this class of models and investigate the corresponding perturbation dynamics. The resulting matter power spectrum for the special case of a time-varying Lambda model is compared with data from the SDSS DR9 catalogue. We find a best-fit value of $xi = 3.25$ which corresponds to a decay of dark matter into the cosmological term. Our results are compatible with the $Lambda$CDM model at the 2$sigma$ confidence level.
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We show that the f(T) gravitational paradigm, in which gravity is described by an arbitrary function of the torsion scalar, can provide a mechanism for realizing bouncing cosmologies, thereby avoiding the Big Bang singularity. After constructing the simplest version of an f(T) matter bounce, we investigate the scalar and tensor modes of cosmological perturbations. Our results show that metric perturbations in the scalar sector lead to a background-dependent sound speed, which is a distinguishable feature from Einstein gravity. Additionally, we obtain a scale-invariant primordial power spectrum, which is consistent with cosmological observations, but suffers from the problem of a large tensor-to-scalar ratio. However, this can be avoided by introducing extra fields, such as a matter bounce curvaton.
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