Transition temperature(s) of magnetized two-flavor holographic QCD

Abstract

During heavy ion collisions, high temperatures and strong magnetic fields are generated. We employ the gauge-gravity duality to study the N-f = 2 QCD phase diagram under these extreme conditions in the quenched approximation; in particular we use the non-antipodal Sakai-Sugimoto model (SSM). We take the different coupling of up and down flavors to the magnetic field into account geometrically, resulting in a split of the chiral phase transition according to flavor. We discuss the influence of the magnetic field on the chiral temperatures-in physical GeV units-in terms of the choice of the confinement scale in the model, extending hereby our elsewhere presented discussion of fixing the non-antipodal SSM parameters to the deconfinement phase. The flavor-dependent (T, L, eB) phase diagram, with variable asymptotic brane-antibrane separation L, is also presented, as a direct generalization of the known (T, L) phase diagram of the non-antipodal SSM at zero magnetic field. In particular, for sufficiently small L we are probing a Nambu-Jona-Lasinio (NJL)-like boundary field theory in which case we do find results very reminiscent of the predictions in NJL models

Superconducting properties of vacuum in strong magnetic field

“…[38,39]. Signatures of this unusual effect were also found in holographic approaches [40][41][42][43] and in numerical simulations of quenched lattice QCD. 44 A possibility of the ⇢-meson condensation was also briefly mentioned in Ref.…”

“…Although a first-principle treatment of this problem is impossible due to strong nonperturbative effects, the superconducting phase was shown to exist in various effective models of QCD such that effective bosonic ⇢-meson electrodynamics, 35, 36 the effective fermionic Nambu-Jona-Lasinio model 38, 39 and in different holographic approaches. [40][41][42][43] There are also signatures of the superconducting/superfluid phase in numerical simulations of lattice QCD. …”

“…Although a first-principle treatment of this problem is impossible due to strong nonperturbative effects, the superconducting phase was shown to exist in various effective models of QCD such that effective bosonic ⇢-meson electrodynamics, 35,36 the effective fermionic Nambu-Jona-Lasinio model 38,39 and in different holographic approaches. [40][41][42][43] There are also signatures of the superconducting/superfluid phase in numerical simulations of lattice QCD. 44,45 As the background magnetic field strengthens further, the electroweak sector of the Standard Model may also experience another superconducting, and, simultaneously, superfluid transition associated with a condensation of, respectively, the W and Z bosons at a critical magnetic field of the electroweak scale, B EW ⇠ 10 20 T. The condensation of the W bosons -first predicted by Ambjørn and Olesen in Refs.…”

Inverse magnetic catalysis in bottom-up holographic QCD

“…Background U(1) B electromagnetic fields are introduced into AdS/CFT via sources for the operatorqγ µ q [50][51][52][53][54]. These operators are described by a bulk, massless U(1) gauge field.…”

“…There is no clear controlled power counting in such effective field theories but they nevertheless provide some insight into the dynamics and quantitative behaviour of the gauge dynamics. The effects of magnetic field in gauge theories with known duals has been studied in [50][51][52][53][54]. [55] has explored the effect of magnetic field on the deconfinement transition associated in holography with the transition to a geometry with a black hole.…”