Collapsed structures in scalar-tensor theories of gravity
PT-CERN Call 2020/2
Instituto Superior Técnico (Universidade de Lisboa)
CENTRA - Center for astrophysics and gravitation
Many beyond the Standard Model theories introduce novel scalar degrees of freedom in order to explain inflation, dark energy and dark matter. Interestingly enough, these fields could play an important role not only on the dynamics of the Universe as a whole but also on the evolution of collapsed structures such as galaxies or stars. In particular, the presence of additional scalar degrees of freedom gives rise, almost generically, to new attractive forces able to modify the standard gravitational collapse of General Relativity. Depending on the precise couplings to matter, this modification could allow for unexpected phenomena such as the formation of primordial black holes during radiation domination or the existence of neutron stars with scalar hairs on spherically symmetric backgrounds. This PhD thesis focuses on the role of scalar interactions on the formation and evolution of compact structures in the early and late Universe. By using analytical and numerical techniques, we will study aspects such as the dynamical development of the screening mechanism, the formation and stability of structures with scalar hair and the impact of fifth forces on the formation and evolution of stars. In particular, we are interested in models involving universal and non-universal couplings to the visible and dark matter sectors. Our studies could have a strong impact on our understanding of the relation between dark energy and dark matter while being relevant for current and future astrophysical and cosmological surveys such as GAIA.