tremendously successful, however, in order to explain the observational data, the matter in the universe must be dominated today by two mysterious dark components (dark matter and dark energy), in fact visible matter such as stars, planets and people accounts for just 4% of the total content of the universe. For many physicists this represents a major problem. In a nutshell, if GR is correct, we understand the dynamics of the universe but do not have a good understanding of what it is made of. The motivation for developing alternative descriptions to gravity, which does away with the need for dark matter and/or dark energy, is therefore very compelling.

My research programme addresses one of the most important problems in modern Cosmology:  the nature of the gravitational action and how changing it could provide a solution to the dark energy and dark matter problems. General Relativity (GR) is one of the cornerstones of modern physics. It describes in mathematical terms how matter causes space-time to curve, and therefore how objects in the universe move in a gravitational field. In particular it provides the foundations on which the standard model of cosmology is built. This picture has been