Inverse magnetic catalysis induced by sphalerons

TL;DR

This paper proposes that sphaleron-induced chiral imbalance explains the inverse magnetic catalysis observed near the QCD critical temperature, revealing new insights into magnetic effects on chiral phase transitions.

Contribution

It introduces a sphaleron-based mechanism for inverse magnetic catalysis, connecting topological transitions to chiral symmetry restoration in strong magnetic fields.

Findings

Sphaleron transitions cause chiral imbalance at high temperatures.

Magnetic fields enhance chiral imbalance, lowering the critical temperature.

The mechanism explains inverse magnetic catalysis at finite baryon density.

Abstract

The recently discovered inverse magnetic catalysis around the critical temperature indicates that some important information is missing in our current understanding of conventional chiral dynamics of QCD, which is enhanced by the magnetic field. In this work, we provide a mechanism to explain that the inverse magnetic catalysis around the critical temperature is induced by sphalerons. At high temperatures, sphaleron transitions between distinct classical vacua cause an asymmetry between the number of right- and left-handed quarks due to the axial anomaly of QCD. In the presence of a strong magnetic field, the chiral imbalance is enhanced and destroys the right- and left-handed pairings, which naturally induces a decreasing critical temperature of the chiral phase transition for increasing magnetic field. The inverse magnetic catalysis at finite baryon density, and the critical end point in the presence of a strong magnetic field is also explored in this work.