Absence of CP Violation in the Strong Interaction: Vacuum thwarts Axion

TL;DR

This paper investigates the absence of CP violation in strong interactions by examining the QCD vacuum's response to the theta term, using lattice methods, and compares it with the axion solution.

Contribution

It presents new lattice-based insights into how the QCD vacuum suppresses CP violation, challenging the axion solution.

Findings

QCD vacuum resists CP violation induced by the theta term

Lattice results support the natural suppression of the theta term effects

Comparison shows limitations of the axion solution in this context

Abstract

QCD admits a contribution to the action, the $\theta$ term, which potentially gives rise to nontrivial phases and violates CP. This is essentially a question of how the vacuum reacts to the $\theta$ term. In this talk I will address the problem using new developments on the lattice. The overall solution is contrasted with the axion `solution'.