The QCD phase diagram for external magnetic fields

Abstract

The effect of an external (electro)magnetic field on the finite temperature transition of QCD is studied. We generate configurations at various values of the quantized magnetic flux with N f = 2 + 1 flavors of stout smeared staggered quarks, with physical masses. Thermodynamic observables including the chiral condensate and susceptibility, and the strange quark number susceptibility are measured as functions of the field strength. We perform the renormalization of the studied observables and extrapolate the results to the continuum limit using N t = 6, 8 and 10 lattices. We also check for finite volume effects using various lattice volumes. We find from all of our observables that the transition temperature T c significantly decreases with increasing magnetic field. This is in conflict with various model calculations that predict an increasing T c (B). From a finite volume scaling analysis we find that the analytic crossover that is present at B = 0 persists up to our largest magnetic fields eB ≈ 1 GeV 2 , and that the transition strength increases mildly up to this eB ≈ 1 GeV 2 .

Chiral and deconfinement transitions in a magnetic background using the functional renormalization group with the Polyakov loop

“…In the recent papers [6,24], the authors suggest a resolution of the discrepancy between the model calculations and the lattice simulations. The chiral condensate can be written as …”

“…At zero µ B and finite B, there is no sign problem and so one can calculate the phase diagram in the T, B plane using Monte-Carlo methods. Recent lattice calculations [6,7] suggest that for physical quark masses, the transition temperature for the chiral transition is a decreasing function of the magnetic field B, while for larger values of the quark masses corresponding to m π ≃ 400 MeV, the temperature is an increasing function of B [8,9]. The qualitative behavior of the transition temperature for physical quark masses is in disagreement with model calculations using either the (Polyakov-loop extended) Nambu-Jona-Lasinio ((P)NJL) model or the (Polyakov-loop extended) quarkmeson model ((P)QM); in these models, the critical temperature is an increasing function of the magnetic field, see e.g.…”

Phase transition and critical end point driven by an external magnetic field in asymmetric quark matter

“…Fields of this intensity affect the QCD phase diagram as shown in [6]. Therefore, understanding the effect of an external magnetic field on the structure of the QCD phase diagram is very important, and this has already led to several studies [7][8][9][10][11][12][13], in particular, at zero chemical potential μ ¼ 0 (the T − eB plane); see [14][15][16][17] for a review.…”

One-loop QCD thermodynamics in a strong homogeneous and static magnetic field

“…Therefore the longitudinal component (3.36) gives the Debye mass (3.16) for the massless quarks, 38) which was recently obtained by one of us [64] and also by others using the different approaches [33,65]. Thus the Debye mass in the presence of a strong magnetic field depends…”

“…Recently the lattice QCD simulations [36] have explored the effects of background magnetic fields on the equation of state (EoS) by calculating the thermodynamic observables, namely the transverse and longitudinal pressures, the magnetization, the energy density, the entropy density etc. and have inferred that the transition temperature is reduced by the presence of a magnetic field [37][38][39][40][41][42]. Similarly the effects of strong magnetic fields on the phase structures of the hadronic matter have been reviewed in [23] through the low-energy effective theories, where the thermodynamic quantities are also found to increase with the magnetic field [43].…”