S. Capozziello, M. De Laurentis, G. Lambiase
The cosmological consequences of the f(R) gravity are reviewed in the
framework of recent data obtained by PAMELA (Payload for Antimatter Matter
Exploration and Light-nuclei Astrophysics) experiment. This collaboration has
reported an excess of positron events that cannot be explained by conventional
cosmology and particle physics, and are usually ascribed to the dark matter
presence (in particular, weak interacting massive particles). The dark matter
interpretation of PAMELA data has motivated the study of alternative
cosmological models (with respect to the standard cosmology) owing to the fact
that they predict an enhancement of the Hubble expansion rate, giving rise in
such a way to thermal relics with a larger relic abundance. In this paper we
face this problem for f(R) gravity models assuming a power law correction to
the standard action of General Relativity, i.e. f(R) = R + \alpha R^n. In the
regime in which the energy density induced by (higher order) curvature terms
are greater than (or of the order of) the energy density of standard radiation,
we find that the exponent n must assume values n > 1. In the opposite regime,
taking into account the constraints provided by big bang nucleosynthesis, we
get n < 1 + 2 \times 10^-3. The latter bound excludes the model f(R) = R +
\alpha R^2. Our analysis shows that the considered model allows to explain the
PAMELA puzzle for dark matter relic particles with masses greater or lesser
than 10^2 GeV.
View original:
http://arxiv.org/abs/1201.2071
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