Cosmological density perturbations in modified gravity theories

Details Cosmological density perturbations in modified gravity theories Cosmological density perturbations in modified gravity theories

2008-12-16

arxiv.org/abs/0812.3048v1

Astronomy and Astrophysics

Astrophysics

4 pages, 2 figures. Contribution to the proceedings of Spanish Relativity Meeting 2008, Salamanca, Spain, 15-19 September 2008

Scientific paper

In the context of f(R) theories of gravity, we study the cosmological evolution of scalar perturbations by using a completely general procedure. We find that the exact fourth-order differential equation for the matter density perturbations in the longitudinal gauge, reduces to a second-order equation for sub-Hubble modes. This simplification 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 f(R) adequately describing the present phase of accelerated expansion and satisfying local gravity tests, it does give a correct description for the evolution of perturbations.

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