Speaker
Description
Extensions of $\Lambda$CDM with interactions between dark matter and dark energy are a promising route to address the current cosmic tensions. In this talk, I will discuss interacting dark sector models with entropy couplings, which give rise to pure-momentum transfer in cosmology. While the background evolution is unchanged, the models are characterised by distinct observational signatures at the level of cosmological perturbations. I show that the couplings lead to a late-time suppression of structure growth while remaining compatible with CMB measurements, which is especially relevant for addressing the $S_8$ tension. I will then discuss the theoretical viability of these types of interactions and observational constraints from current survey data.