A possible anthropic solution to the Strong CP problem

TL;DR

This paper proposes an anthropic approach to the strong CP problem by linking it to the cosmological constant problem, suggesting explicit symmetry breaking and a probability distribution favoring higher vacuum energies.

Contribution

It introduces a novel anthropic solution to the strong CP problem by connecting it with the cosmological constant problem and allowing explicit Peccei-Quinn symmetry breaking.

Findings

The mechanism avoids cosmological issues of large-scale axions.

Explicit symmetry breaking gives axions a large mass.

Probability distribution favors higher vacuum energies.

Abstract

We point out that the long-standing strong CP problem may be resolved by an anthropic argument. The key ideas are: (i) to allow explicit breaking(s) of the Peccei-Quinn symmetry which reduces the strong CP problem to the cosmological constant problem, and (ii) to conjecture that the probability distribution of the vacuum energy has a mild pressure towards higher values. The cosmological problems of the (s)axion with a large Peccei-Quinn scale are absent in our mechanism, since the axion acquires a large mass from the explicit breaking.