Hans A. Winther
Institute of Theoretical Astrophysics, University of Oslo

Abstract
The accelerated expansion of the Universe, coined dark energy, might be due to a modifications of gravity on large scales. The simplest possibility involves a scalar field coupled to matter.

Light scalar fields are a vital ingredient in many theories beyond the standard model. These fields are expected to couple to matter which would imply a fifth-force in nature.

General Relativity is well tested in the solar-system, and the results naively tell us that if a fifth-force exists then it must be much weaker than gravity or have a sub-millimeter range.

This can be elevated if the scalar field employs a screening mechanism which is way of suppressing the effects of the fifth-force in high density environments where experiments are performed, while at the same time allows for a long-range force comparable in strength to gravity on large scales.

Due to a high degree of non-linearity in the field-equations N-body simulations are generally required to gain quantitative insight in the effects on structure formation in such models. This represents a big challenge to numerical codes and computation resources.

However, these studies are worthwhile and have revealed a plethora of signatures which can in principle be detected both by near future gravity experiments and in cosmological observations (like EUCLID).

We will go through the phenomenology of modified gravity theories, present results from N-body simulations and discuss interesting signatures found in these models.

2012 June 15, 13:30

IA/U.Porto
Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto