Orador: Álvaro de la Cruz-Dombriz (Astrophysics, Cosmology and Gravity Centre (ACGC), University of Cape Town). Data, hora e local: 17 de Novembro de 2015, às 11h30m na sala de reuniões do Departamento de Matemática.

Resumo: Modified gravity has attracted much attention over the last few years and remains a competitive candidate for dark energy. In particular, the so-called viable f(R) gravity theories, which are able to both recover General Relativity (GR) and produce late-time cosmic acceleration, have been widely studied in recent literature. Nevertheless, extended theories of gravity suffer from several shortcomings which compromise their ability to provide realistic alternatives to the standard cosmological Lambda-CDM Concordance model. We address the existence of cosmological singularities and the conditions that guarantee late-time acceleration, assuming reasonable energy conditions for standard matter in the so-called Hu-Sawicki f(R) model, currently among the most widely studied modifications to General Relativity. I will present the
dynamical systems perspective which serves to fully solve the background equations and provide qualitative information regarding the phase space of this model. Several stable de Sitter equilibrium points are identified, as well as one unstable matter-like point and solution orbits which resemble the CDM evolution. Then using the Supernovae Ia Union 2.1 catalogue, I shall show how further constraints on the free parameters of this model can be obtained. The combined analysis of both theoretical and observational constraints sheds some light on the viable parameter space of these models and the form of the underlying effective theory of gravity.

Funded by the Portuguese Government through the FCT – Fundação para a Ciência e a Tecnologia under the project UID/MAT/00212/2013