COSMOLOGICAL AND SOLAR-SYSTEM TESTS OF f(R) MODIFIED GRAVITY

We, the LeCosPA Dark Energy Working Group, are investigating dark energy and modified gravity as possible origins of the accelerating expansion of the present universe. In this paper we report our recent progress in modified gravity, in particular the work in arXiv:1009.3488 on the cosmological and the solar-system tests of the f(R) theory of modified gravity. In this work we found that the solar-system test ruled out the frequently studied w = -1 designer f(R) models which are cosmologically distinct from the Lambda CDM model. In addition, under the cosmological test many designer f(R) models suffer a fine-tuning problem about the choice of the initial condition of f(R).