Response of Holographic QCD to Electric and Magnetic Fields

TL;DR

This paper investigates how the Sakai-Sugimoto holographic model of large N_c QCD responds to external electric and magnetic fields, revealing phase transitions, conductivity behavior, and effects on chiral symmetry restoration.

Contribution

It introduces new embeddings for baryonic conductors and provides detailed analysis of phase transitions and susceptibilities under external fields in holographic QCD.

Findings

First-order insulator-conductor transition in electric fields

Conductivity matches Kubo formula calculations

Critical temperature for chiral restoration increases with magnetic field

Abstract

We study the response of the Sakai-Sugimoto holographic model of large N_c QCD at nonzero temperature to external electric and magnetic fields. In the electric case we find a first-order insulator-conductor transition in both the confining and deconfining phases of the model. In the deconfining phase the conductor is described by the parallel 8-brane-anti-8-brane embedding with a current of quarks and anti-quarks. We compute the conductivity and show that it agrees precisely with a computation using the Kubo formula. In the confining phase we propose a new kind of 8-brane embedding, corresponding to a baryonic conductor. In the magnetic field case we show that the critical temperature for chiral-symmetry restoration in the deconfined phase increases with the field and approaches a finite value in the limit of an infinite magnetic field. We also illustrate the nonlinear behavior of the electric and magnetic susceptibilities in the different phases.