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arXiv · 0802.2999

On the evolution of density perturbations in f(R) theories of gravity

A. de la Cruz-Dombriz·A. Dobado·A. L. Maroto
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Abstract

In the context of $f(R)$ theories of gravity, we study the evolution of scalar cosmological perturbations in the metric formalism. Using a completely general procedure, we find the exact fourth-order differential equation for the matter density perturbations in the longitudinal gauge. In the case of sub-Hubble modes, the expression reduces to a second-order equation which is compared with the standard (quasi-static) equation used in the literature. We show that for general $f(R)$ functions the quasi-static approximation is not justified. However, for those functions adequately describing the present phase of accelerated expansion and satisfying local gravity tests, it provides a correct description for the evolution of perturbations.

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A. de la Cruz-Dombriz, A. Dobado, A. L. Maroto. 2008-06-05. On the evolution of density perturbations in f(R) theories of gravity. https://doi.org/10.1103/physrevd.77.123515

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