Magnetic catalysis and the chiral condensate in holographic QCD

Abstract

We investigate the effect of a non-zero magnetic field on the chiral condensate using a holographic QCD approach. We extend the model proposed by Iatrakis, Kiritsis and Paredes in [1] that realises chiral symmetry breaking dynamically from 5d tachyon condensation. We calculate the chiral condensate, magnetisation and susceptibilities for the confined and deconfined phases. The model leads, in the probe approximation, to magnetic catalysis of chiral symmetry breaking in both confined and deconfined phases. In the chiral limit, mq = 0, we find that in the deconfined phase a sufficiently strong magnetic field leads to a second order phase transition from the chirally restored phase to a chirally broken phase. The transition becomes a crossover as the quark mass increases. Due to a scaling in the temperature, the chiral transition will also be interpreted as a transition in the temperature for fixed magnetic field. We elaborate on the relationship between the chiral condensate, magnetisation and the (magnetic) free energy density. We compare our results at low and moderate temperatures with lattice QCD results.

On the interplay between magnetic field and anisotropy in holographic QCD

“…This was shown at zero B and at c = 0.4 in [26], and continues to hold at finite B as well as for c = 0.25. We also note that in a related model [58,59], where chiral symmetry breaking arises as in V-QCD through a tachyonic brane action but backreaction is not considered, only magnetic catalysis was found [60]. This result agrees with our earlier work, where backreaction was seen to be essential for inverse magnetic catalysis [48].…”

Holographic model for heavy quarks in anisotropic hot dense QGP with external magnetic field

“…In the holographic approach light/heavy quarks models have different structures of the background phase transition [16,28]. In most of holographic models the background phase transition, see figure 17 A, is related to chiral symmetry breaking [15,22,24,33,34,40,41,44,48,49,51]. Confinement/deconfinement phase transition may be related to background phase transition and may be not, figure 17 B.…”

“…Isotropic holographic QCD "bottom-up" models were considered in numerous papers [6]- [55]. These models have been considered to study the confinement/deconfinement phase transition [6-8, 11, 13, 16-21, 23, 31, 32, 35, 38, 49, 53-55], as well as the chiral phase transition [15,22,24,33,34,40,41,44,48,49,51] and also to search for quarkyonic phase transition [37]. One of the popular methods for constructing an HQCD within the "bottom-up" approach is a potential reconstruction method for models with Einsteindilaton-Maxwell action.…”

Holographic anisotropic model for light quarks with confinement-deconfinement phase transition

“…There are several reasons to consider anisotropic versions of the holographic models mentioned above: to reproduce the experimental data for the energy dependence of the total multiplicity [17], to describe inverse magnetic catalysis [30,[34][35][36][37] or to take into account anisotropic geometry of colliding ions. In [38] the anisotropic holographic model for heavy quarks was studied.…”