Orateur
Description
In the standard LCDM model, dark matter (DM) and dark energy (DE) are treated as independent components of the Universe. Dark matter is modelled as a pressureless fluid, while dark energy is described by a constant vacuum energy density. Despite this phenomenological separation, it is conceivable that both components share a common physical origin. In this talk, I will present three models of the dark sector in which both dark matter and dark energy are described by scalar fields that interact through potential terms, conformal couplings, kinetic couplings, or combinations thereof. The first model demonstrates that a hybrid inflation-inspired potential provides a very good description of the dark sector while introducing only a single additional parameter beyond LCDM. The second, an axion–dilaton model motivated by theories with extra dimensions, identifies dark energy with a dilaton field and dark matter with an axion field. This framework provides a minimal realisation of an interacting dark sector within axion–dilaton theories. Finally, I will discuss a novel scenario in which the interaction between dark matter and dark energy is mediated by the dark matter field rather than the dark energy field. This leads to qualitatively different dark matter phenomenology: in particular, dark matter is no longer pressureless, and its pressure can become negative at late cosmic times.