Speaker: Lucas Lombriser
Location: Centro Stefano Franscini, Monte Verita, Ascona, Switzerland
Cosmic acceleration may be attributed to a scalar field, which could couple to matter and modify the gravitational interactions. While enhancing gravity on large scales, nonlinear mechanisms such as the chameleon effect can suppress the modification in high-density regions and make it compatible with Solar System tests. The transition between these two regimes provides a unique signature on cluster scales and a great probe of gravity. With special emphasis on f(R) gravity, I discuss the formation of structure in chameleon theories based on the spherical collapse model and excursion set theory with a mass- and environment-dependent barrier approximated by the thin-shell thickness of the chameleon transition. In combination with N-body simulations, these results can be used to efficiently model modifications in, e.g., the halo-mass function, differences between dynamical and lensing masses, and environmental effects for the comparison to observations.