Dilaton dominance in the early Universe dilutes Dark Matter relic abundances

TL;DR

This paper explores how a dilaton field in the early universe can dilute dark matter relic densities, potentially reconciling experimental constraints with supersymmetric models by competing mechanisms that decrease relic abundance.

Contribution

It introduces a general framework for dilaton-induced relic density dilution, contrasting with quintessence scenarios, and analyzes its implications for dark matter detection.

Findings

Dilaton coupling to matter can significantly reduce dark matter relic densities.

The dilution mechanism can reconcile small neutralino-nucleon cross sections with relic abundance constraints.

Dilaton effects are significant only in the early universe, before Big Bang Nucleosynthesis.

Abstract

The role of the dilaton field and its coupling to matter may result to a dilution of Dark Matter (DM) relic densities. This is to be contrasted with quintessence scenarios in which relic densities are augmented, due to modification of the expansion rate, since Universe is not radiation dominated at DM decoupling. Dilaton field, besides this, affects relic densities through its coupling to dust which tends to decrease relic abundances. Thus two separate mechanisms compete each other resulting, in general, to a decrease of the relic density. This feature may be welcome and can rescue the situation if Direct Dark Matter experiments point towards small neutralino-nucleon cross sections, implying small neutralino annihilation rates and hence large relic densities, at least in the popular supersymmetric scenarios. In the presence of a diluting mechanism both experimental constraints can be met. The role of the dilaton for this mechanism has been studied in the context of the non-critical string theory but in this work we follow a rather general approach assuming that the dilaton dominates only at early eras long before Big Bang Nucleosynthesis.