No inverse magnetic catalysis in the QCD hard and soft wall models

TL;DR

This study investigates the effects of magnetic fields on holographic QCD models, confirming the absence of inverse magnetic catalysis in the chiral transition and highlighting the complexities in modeling QCD phenomena holographically.

Contribution

It demonstrates that the soft wall holographic model does not exhibit inverse magnetic catalysis at the chiral transition, contrasting with some lattice QCD results.

Findings

Decreasing deconfinement temperature with magnetic field.

No evidence of inverse magnetic catalysis in the chiral transition.

Identification of complications in holographic modeling of QCD.

Abstract

In this paper, we study the influence of an external magnetic field in holographic QCD models where the backreaction is modeled in via an appropriate choice of the background metric. We add a phenomenological soft wall dilaton to incorporate better IR behavior (confinement). Elaborating on previous studies conducted by [JHEP 1505 (2015) 121], we first discuss the Hawking-Page transition, the dual of the deconfinement transition, as a function of the magnetic field. We confirm that the critical deconfinement temperature can drop with the magnetic field. Secondly, we study the quark condensate holographically as a function of the applied magnetic field and demonstrate that this model does not exhibit inverse magnetic catalysis at the level of the chiral transition. The quest for a holographic QCD model that qualitatively describes the inverse magnetic catalysis at finite temperature is thus still open. Throughout this work, we pay special attention to the different holographic parameters and we attempt to fix them by making the link to genuine QCD as close as possible. This leads to several unanticipated and so far overlooked complications (such as the relevance of an additional length scale in the confined geometry) that we discuss in detail.