Inverse magnetic catalysis in QCD and holography

Abstract

A holographic model of a QCD-like theory in a magnetic background is studied in the limit of an infinite number of colors Nc and infinite massless quark flavors Nf, where the ratio x = Nf/Nc is kept constant at 1. The gravitational model contains two scalar bulk fields, namely a dilaton λ, which is the source of tr F^2 , with F the gluon field tensor, and a tachyon sourcing the chiral condensate <q̄q>. This model is used to compute both the chiral and the deconfinement phase transition temperatures, as well as the chiral condensate. This leads to a computation of the phase diagram of QCD in the (T, B)-plane, as well as the observation of inverse magnetic catalysis of the chiral condensate by the magnetic field, in qualitative agreement with lattice results.