Coupled Quintessence and the Halo Mass Function

TL;DR

This paper investigates how coupled quintessence models influence the halo mass function and cluster formation, comparing predictions to observations and assessing their viability as alternatives to Lambda-CDM cosmology.

Contribution

It provides semi-analytic predictions for halo abundance in coupled quintessence models and compares these to Lambda-CDM, including a global fit to observational data.

Findings

Coupled quintessence models can match or differ from Lambda-CDM in predicting massive high-redshift clusters.

Energy flow from quintessence to dark matter generally reduces halo abundance compared to Lambda-CDM.

Some models fit observational data well, offering viable alternatives to Lambda-CDM.

Abstract

A sufficiently light scalar field slowly evolving in a potential can account for the dark energy 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. Using semi--analytic expressions for the CDM halo mass function, we make predictions for halo abundance in models where the quintessence scalar field is coupled to cold dark matter, for a variety of quintessence potentials. We evaluate the linearly extrapolated density contrast at the redshift of collapse using the spherical collapse model and we compare this result to the corresponding prediction obtained from the non--linear perturbation equations in the Newtonian limit. For all the models considered in this work, if there is a continuous flow of energy from the quintessence scalar field to the CDM component, then the predicted number of CDM haloes can only lie below that of $\Lambda$CDM, when each model shares the same cosmological parameters today. In the last stage of our analysis we perform a global MCMC fit to data to find the best fit values for the cosmological model parameters. We find that for some forms of the quintessence potential, coupled dark energy models can offer a viable alternative to $\Lambda$CDM in light of the recent detections of massive high--$z$ galaxy clusters, while other models of coupled quintessence predict a smaller number of massive clusters at high redshift compared to $\Lambda$CDM.