CP3 Lunch - A catch 22 for large distance modifications of gravity - Karel Van Acoleyen

by Dr Karel Van Acoleyen (Universiteit Gent)

Wednesday 4 Mar 2009, 13:00 → 13:50 Europe/Brussels

Cycl.06

In this talk I will first show why, in the context of ordinary gravity, the influence of the small scale structure (stars, galaxies, clusters,...) on the large scale gravitational dynamics of our Universe, the so called backreaction, is very small. I will then argue that this is not the case anymore for different large distance modifications of gravity, including the DGP model, f(R,GB) gravity and the chameleon model, that have been put forward as alternatives to dark energy. For those models, the very same mechanism that turns off the modification of the gravitational force at short distances, as required by the Solar System constraints, generates a large backreaction. This seems to render any semi-analytic understanding of the cosmology for these models virtually impossible, since the conventional FLRW framework would break down completely.