A momentum coupling between dark matter and dark energy : consequences at small scales

Abstract

Dark energy is frequently modelled as an additional dynamical scalar field component in the Universe, referred to as “quintessence,” which drives the late-time acceleration. Furthermore, the quintessence field may be coupled to dark matter and/or baryons, leading to a fifth force. In this thesis we explore the consequences for non-linear cosmological structure formation arising from a momentum coupling between the quintessence field and dark matter. The coupling leads to a modified Euler equation, which we implement in an N-body cosmological simulation. We then analyse the non- linear power spectrum, comparing with the standard ΛCDM cosmology, as well as the halo mass function, and various other dark matter halo properties. We find that, for certain quintessence potentials, a positive coupling leads to a large enhancement of structure formation at small scales.