Coupled Quintessence and the Halo Mass Function
Tarrant, Ewan (University of Nottingham)

A sufficiently light scalar field slowly rolling in a potential can account for the dark energy density that presently dominates the universe. This quintessence field is expected to couple directly to matter components, unless some symmetry of a more fundamental theory protects or suppresses it. Such a coupling would leave distinctive signatures in the background expansion history of the universe and on cosmic structure formation, particularly at galaxy cluster scales. With the arrival of greatly improved high redshift cluster surveys such as the Dark Energy Survey (DES) and Planck, the mass distribution of the most massive objects in the Universe is a powerful tool which may be used to distinguish between different models of dark energy. Using semi--analytic expressions for the CDM halo mass function we make predictions for halo abundance in coupled quintessence cosmologies. We find that, depending on the form of the quintessence potential and the strength of the coupling, the predicted number of haloes at a given epoch of a given mass, can lie above or below that of Lambda--CDM.