Generating the Dark Matter mass from the QCD vacuum: A new approach to the Dark Matter-Baryon coincidence problem

TL;DR

This work proposes a novel mechanism whereby a colorless dark matter particle acquires a GeV-scale mass from the QCD vacuum via vacuum misalignment in a strongly coupled dark sector. A two-scale condensate structure and QCD-triggered misalignment generate an ${\cal O}(1)$ GeV dark matter, accompanied by dark pions and a composite QCD axion with decay constant $f_a=\frac{\sqrt{21}}{5}f_D$, all embedded in a UV-complete double 54321 framework. The UV completion yields a dark baryon $X$ whose mass derives from the QCD vacuum, and a rich pNGB spectrum including the light complex dark pion $\Pi'$ and the axion, with $f_E=f_D$ tying the scales of the dark gauge sector. Cosmology is discussed in an ADM context, with BBN and astrophysical bounds restricting $f_D$ to a finite viable range, while future ALP and direct-detection experiments could probe the remaining parameter space and test the link between QCD vacuum structure and the dark sector.

Abstract

The comparable abundances of dark matter and baryons imply a deep connection between the dark sector and the QCD sector. In models of asymmetric dark matter, the number densities of both sectors are ensured to be similar. However, a complete solution should also include a mechanism for comparable masses. In this letter, we present a solution based on a strongly coupled chiral dark sector, featuring a light composite fermion as the dark matter. Its mass is generated through the misalignment triggered by the QCD vacuum, ensuring the mass to be at the GeV scale. The model features $\mathcal{O}(1)$ GeV dark baryon dark matter together with dark pions (axion-like particles). Moreover, a composite QCD axion naturally arise in the UV model.

Figures (1)

• Figure 1: The Feynman diagram responsible for the mass generation of the dark lepton $\chi$ in the toy model.