Strong CP and SUZ$_2$

Understand

Solutions to the strong CP problem typically introduce new scales associated with the spontaneous breaking of symmetries.

• Absent any anthropic argument for small $\bar\theta$, these scales require stabilization against ultraviolet corrections.
• Supersymmetry offers a tempting stabilization mechanism, since it can solve the "big" electroweak hierarchy problem at the same time.
• One family of solutions to strong CP, including generalized parity models, heavy axion models, and heavy $\eta^\prime$ models, introduces $\mathbb{Z}_2$ copies of (part of) the Standard Model and an associated scale of $\mathbb{Z}_2$-breaking.