Phantom behaviour and growth index anomalous evolution in viable f(R) gravity models
Abstract
We present numerical calculation of the evolution of a background space-time metric and sub-horizon matter density perturbations in viable f(R) gravity models of present dark energy and cosmic acceleration. We found that viable models generically exhibit recent crossing of the phantom boundary wDE=-1. Moreover, as a consequence of the anomalous growth of density perturbations during the end of the matter-dominated stage, their growth index evolves non-monotonically with time and may even become negative.
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