Wednesday seminar: Hans A. Winther

Scalar fields, strongly coupled to matter, can be present in nature and still be invisible to local experiments if they are subject to a screening mechanism. The Symmetron is one such mechanism which relies on restoration of a spontaneously broken symmetry in regions of high density to shield the scalar fifth force. We have investigated structure formation with Symmetron fields by using N-body simulations and find that observable signatures exists in both the linear and nonlinear matter power spectrum and on the halo mass function for a large range of model parameters that are within what is allowed by local gravity experiments. We have further investigated the environment dependence of dark matter halos in this modified gravity scenario. The effectiveness of the screening mechanism depends on both the mass of the halo and the environment it lies in and we find a significant difference between the lensing and dynamical mass of dark matter halos similar to what has been found recently in f(R) modified gravity. This signature, which is a smoking gun for modified gravity, can hopefully be probed by near-future high-quality observations.