Testing Modifications of General Relativity with Cosmological Observations

Lucas Lombriser
University of Zurich


Cosmic acceleration can either be explained by introducing large amounts of dark energy or considering modifications to gravity. I present a Markov chain Monte Carlo analysis of the self-accelerating and normal branch of Dvali-Gabadadze-Porrati (DGP) braneworld gravity as well as of metric f(R) gravity. Utilizing a variety of cosmological data sets, both DGP branches require a brane tension or a cosmological constant at high significance with no evidence for the unique DGP modifications. The f(R) gravity models of interest here are designed to reproduce the LCDM expansion history with modications to gravity described by a supplementary cosmological freedom, the Compton wavelength parameter B0. Cosmological observations, primarily from cluster abundance, yield tight constraints on the viable parameter values of B0.