A Proof of the Axion?

Understand

We show that the de Sitter quantum breaking bound when applied to QCD exposes the necessity of the axion solution to the strong CP problem.

• The Peccei-Quinn mechanism emerges as a consistency requirement independent of the naturalness questions.
• The $\theta$-angle must be unphysical rather than simply small.
• All other approaches including a fine-tuning of $\theta$ lead to the existence of de Sitter vacua and are excluded by consistency.