Modified Theories of Gravity

In recent years the overwhelming amount of observational data supporting the \emph{late-time accelerated expansion of the Universe} has thrusted cosmology in particular and gravitation in general to the forefront of scientific research. In fact the problem of the origin of the so called \emph{dark energy} stands as one of the most tantalizing scientific issues of today's theoretical investigations both in the field of fundamental physics and in that of astrophysics. In this context note must be given to the appearance of modifications of Einstein's General Relativity especially designed to deal with this problem although simultaneously addressing other inconsistencies of the standard view of gravity such as the dark matter problem and inflation. This is the case of the scalar-tensor theories of gravity and the $f(R)$ modified theories of gravity. In this work we consider these modifications but focus on the existence of a specific type of exact solution: traversable wormholes. These are hypothetical tunnels in space-time and are primarily useful as ``gedanken-experiments and as a theoreticians probe of the foundations of general relativity although their existence as