Spontaneous generation of local CP violation and inverse magnetic catalysis

TL;DR

This paper explores how instanton--anti-instanton molecules induce local CP violation and chiral imbalance in QCD, showing that magnetic fields lower the critical temperature and promote inverse magnetic catalysis.

Contribution

It demonstrates that polarized instanton--anti-instanton pairing causes spontaneous local CP violation and explains inverse magnetic catalysis through a new mechanism involving axial-vector interactions.

Findings

External magnetic fields lower the critical temperature for CP violation.

Magnetic fields catalyze chiral imbalance and suppress chiral condensate.

A repulsive axial-vector interaction explains inverse magnetic catalysis.

Abstract

In the chiral symmetric phase, the polarized instanton--anti-instanton molecule pairing induces a nontrivial repulsive interaction in the iso-scalar axial-vector channel. As a consequence, one unusual property is observed that in the chiral restoration phase, there is a first order phase transition for the spontaneous generation of local CP violation and chiral imbalance. Furthermore, it is found that external magnetic fields will lower the critical temperature for the local CP-odd phase transition and catalyze the chiral imbalance, which destroys the chiral condensate with pairing quarks between different chiralities. A reasonable strength of the repulsive interaction in the iso-scalar axial-vector channel can naturally explain the inverse magnetic catalysis around the critical temperature under external magnetic fields.