Magnetic catalysis and inverse magnetic catalysis in QCD

TL;DR

This paper explores how strong magnetic fields influence the QCD phase structure, revealing magnetic catalysis at very high fields and inverse catalysis at intermediate levels, with underlying mechanisms analyzed.

Contribution

It provides a detailed numerical and analytical study of magnetic catalysis and inverse catalysis in QCD, highlighting the roles of gluon screening and coupling weakening.

Findings

Magnetic catalysis occurs at very high magnetic fields.

Inverse magnetic catalysis appears at intermediate magnetic fields.

Large magnetic fields turn the chiral transition into a crossover.

Abstract

We investigate the effects of strong magnetic fields on the QCD phase structure at vanishing density by solving the gluon and quark gap equations, and by studying the dynamics of the quark scattering with the four-fermi coupling. The chiral crossover temperature as well as the chiral condensate are computed. For asymptotically large magnetic fields we find magnetic catalysis, while we find inverse magnetic catalysis for intermediate magnetic fields. Moreover, for large magnetic fields the chiral phase transition for massless quarks turns into a crossover. The underlying mechanisms are then investigated analytically within a few simplifications of the full numerical analysis. We find that a combination of gluon screening effects and the weakening of the strong coupling is responsible for the phenomenon of inverse catalysis. In turn, the magnetic catalysis at large magnetic field is already indicated by simple arguments based on dimensionality.