Towards Unquenched Holographic Magnetic Catalysis

TL;DR

This paper develops a holographic model for SU(Nc) N=4 SYM with massless flavors under an external magnetic field, exploring flavor backreaction effects and magnetic catalysis phenomena.

Contribution

It introduces a perturbative string dual model with backreacted flavors and magnetic field, analyzing their impact on meson spectra and background stability.

Findings

Backreacted flavors influence dynamical mass generation.

Strong magnetic fields induce instabilities in the meson spectrum.

The model generalizes previous supersymmetric solutions to include magnetic effects.

Abstract

We propose a string dual to the SU(Nc) N=4 SYM coupled to Nf massless fundamental flavors in an external magnetic field. The flavors are introduced by homogeneously smeared Nf D7-branes and the external magnetic field via a non-trivial Kalb-Ramond B-field. Our solution is perturbative in a parameter that counts the number of internal flavor loops. In the limit of vanishing B-field the background reduces to the supersymmetric one obtained in hep-th/0612118. We introduce an additional probe D7--brane and in the supersymmetric limit of vanishing B-field perform a holographic renormalization of its "on-shell" action. We consider also non-supersymmetric probes with fixed worldvolume gauge field corresponding to a magnetic field coupled only to the fundamental fields of the probe brane. We study the influence of the backreacted flavors on the effect of dynamical mass generation. Qualitatively the physical picture remains unchanged. In the next step we consider the case when the magnetic field couples to both the backreacted and the probe fundamental degrees of freedom. At sufficiently strong magnetic field the meson spectrum signals an instability of the probe D7-brane, which we interpret as reflecting an instability of the supergravity background.