The strong CP problem, general covariance, and horizons

TL;DR

This paper explores how general covariance and horizons in quantum field theory could naturally resolve the strong CP problem by constraining topological sectors without introducing new observable phenomena.

Contribution

It proposes that the constraints from general covariance on topological sectors in QCD could explain the strong CP problem without additional dynamics.

Findings

Topological sectors in QCD can only sum incoherently due to horizon effects.

General covariance constrains the topological structure of quantum field theories.

Potential resolution of the strong CP problem without new particles or forces.

Abstract

We discuss the strong CP problem in the context of quantum field theory in the presence of horizons. We argue that general covariance places constraints on the topological structure of the theory. In particular, as in QCD, it means that different topological sectors of the theory can only sum incoherently, because the degrees of freedom beyond the horizon must be traced over for general covariance to apply. This might lead to a solution of the so-called strong CP problem without extra observable dynamics.