Inverse magnetic catalysis in field theory and gauge-gravity duality

TL;DR

This paper explores inverse magnetic catalysis in QCD-like models, showing how magnetic fields can restore chiral symmetry at finite chemical potential, contrasting with traditional magnetic catalysis, through both holographic and field-theoretical approaches.

Contribution

It provides a comparative analysis of inverse magnetic catalysis in the Sakai-Sugimoto and NJL models, including new analytical results for the NJL model.

Findings

Inverse magnetic catalysis occurs at nonzero chemical potential.

Magnetic fields can restore chiral symmetry.

Comparison between holographic and field-theoretical models.

Abstract

We investigate the surface of the chiral phase transition in the three-dimensional parameter space of temperature, baryon chemical potential and magnetic field in two different approaches, the field-theoretical Nambu-Jona-Lasinio (NJL) model and the holographic Sakai-Sugimoto model. The latter is a top-down approach to a gravity dual of QCD with an asymptotically large number of colors and becomes, in a certain limit, dual to an NJL-like model. Our main observation is that, at nonzero chemical potential, a magnetic field can restore chiral symmetry, in apparent contrast to the phenomenon of magnetic catalysis. This "inverse magnetic catalysis" occurs in the Sakai-Sugimoto model and, for sufficiently large coupling, in the NJL model and is related to the physics of the lowest Landau level. While in most parts our discussion is a pedagogical review of previously published results, we include new analytical results for the NJL approach and a thorough comparison of inverse magnetic catalysis in the two approaches.