In this talk, I will present theories that do not have a de Sitter vacuum and cannot lead to slow-roll quintessence, but which nevertheless support a transient era of accelerated cosmological expansion that can account for Dark Energy. This will be achieved by considering interactions between a scalar and either a hidden sector thermal bath, which evolves as Dark Radiation, an extremely-light component of Dark Matter or a subdominant component of Dark Energy. We show that these simple models can explain the present-day Dark Energy of the Universe consistently with current observations.

Organized by: Catarina Cosme