General Relativity remains to this day our best description of gravitational
phenomena in Nature. The theory has shown remarkable consistency with
observations in
situations ranging from the slowvelocities, weakgravitational fields regime
in the confines of our Solar System, to the highly nonlinear, dynamical
regime
of binary black holes mergers. Despite its tremendous successes, issues
such as
its quantization and the cosmological constant problem suggest Einstein’s
theory
might not be the final theory of the gravitational interaction. Motivated
by these
questions, theorists have proposed a myriad of extension to General
Relativity
over the decades. In this talk, I will focus on theories with additional
scalar degrees of freedom. In particular, I will describe some theories which
pass Solar System tests and yet yield interesting new phenomenology in
stronggravity systems involving compact objects, i.e. neutron stars and
black holes.
