Cosmological consequences of interacting dark energy models

The standard model of cosmology, ΛCDM, is in excellent agreement with almost all present-day cosmological observations, however, there are serious theoretical problems relating to its underpinnings. Moreover, some observations in recent years have caused tensions to arise in the concordance model. It is therefore natural that we look beyond the ΛCDM model and explore the consequences of such extensions. We explore the possibility of dark energy being in the form of a quintessence scalar field and consider an interacting dark energy model whereby the minimally coupled quintessence scalar field is conformally coupled to dark matter. We explore its dynamical evolution and cosmological imprints, and then confront the model with recent cosmological data, finding that the strength of the coupling is constrained to be unappealingly small. This naturally leads to the exploration of new forms of couplings, such as couplings with minima. We show that such a coupling can lead to a growing fifth-force in the dark sector which has been negligible until recent times, with the onset of dark energy domination. We confront this model with cosmological observations and find that background and linear perturbation level data allow for a far stronger fifth-force in comparison. We then venture into cosmology at the smaller, non-linear scale, where we expect that the effects of a growing fifth-force will be highly significant. We conclude by speculating on the role of cosmological N-body simulations in the future of cosmology and the part that growing fifth-force models may play in it.