High quality QCD axion in the Standard Model

Although the axion is the most compelling solution to the strong C P problem, the introduced global Peccei-Quinn symmetry suffers from a severe fine-tuning problem known as the . In this letter, we show that the discrete gauge symmetry Z 4 × Z 3 motivated from the internal structure of the standard model can naturally predict a high-quality axion, leading to a distinct and testable parameter space. Remarkably, this minimal framework simultaneously accounts for neutrino masses, baryon asymmetry, and dark matter.