Theoretical and observational constraints of viable f(R) theories of
  gravity
  Modified gravity has attracted much attention over the last few years and
remains a potential 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. Then using the
Supernovae Ia Union 2.1 catalogue, we further constrain the free parameters of
this model. 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.
