Axionic dark energy and a composite QCD axion

TL;DR

This paper proposes a model where the string theory axion explains dark energy, while a composite QCD axion from hidden sector dynamics could account for dark matter, with their contributions carefully balanced.

Contribution

It introduces a novel scenario combining a model-independent axion for dark energy with a composite QCD axion for dark matter, leveraging hidden sector quark dynamics.

Findings

Hidden sector anomaly contribution is negligible compared to QCD anomaly.

The scenario naturally explains the smallness of dark energy and the presence of dark matter.

The model relies on the presence of many light hidden sector quarks.

Abstract

We discuss the idea that the model-independent (MI) axion of string theory is the source of quintessential dark energy. The scenario is completed with a composite QCD axion from hidden sector squark condensation that could serve as dark matter candidate. The mechanism relies on the fact that the hidden sector anomaly contribution to the composite axion is much smaller than the QCD anomaly term. This intuitively surprising scenario is based on the fact that below the hidden sector scale $\Lambda_h$ there are many light hidden sector quarks. Simply, by counting engineering dimensions the hidden sector instanton potential can be made negligible compared to the QCD anomaly term.