A Theory of Dark Pions

Understand

We present a complete model of a dark QCD sector with light dark pions, broadly motivated by hidden naturalness arguments.

• The dark quarks couple to the Standard Model via irrelevant $Z$- and Higgs-portal operators, which encode the low-energy effects of TeV-scale fermions interacting through Yukawa couplings with the Higgs field.
• The dark pions, depending on their $CP$ properties, behave as either composite axion-like particles (ALPs) mixing with the $Z$ or scalars mixing with the Higgs.
• The dark pion lifetimes fall naturally in the most interesting region for present and proposed searches for long-lived particles, at the LHC and beyond.