Chiral phase structure of three flavor QCD in a background magnetic field

Abstract

We investigate the chiral phase structure of three flavor QCD in a background Uð1Þ magnetic field using the standard staggered action and the Wilson plaquette gauge action. We perform simulations on lattices with a temporal extent of N τ ¼ 4 and four spatial extents of N σ ¼ 8, 16, 20 and 24. We choose a quark mass in lattice spacing as am ¼ 0.030 with corresponding pion mass estimated as m π ∼ 280 MeV such that there exists a crossover transition at vanishing magnetic fields, and adopt two values of magnetic field strength in lattice spacing a ffiffiffiffiffiffi eB p ≃ 1.5 and 2 corresponding to eB=m 2 π ∼ 11 and 20, respectively. We find that the transition becomes stronger in the presence of a background magnetic field, and turns into a first order as seen from the volume scaling of the order parameter susceptibility as well as the metastable states in the time history of the chiral condensate. On the other hand, the chiral condensate and transition temperature always increase with B even within the regime of a first order phase transition. This suggests that the discrepancy in the behavior of chiral condensates and transition temperature as a function of B between earlier lattice studies using larger-than-physical pion masses with standard staggered fermions and those using physical pions with improved staggered fermions is mainly due to lattice cutoff effects.

Fluctuations and correlations of net baryon number, electric charge and strangeness in a background magnetic field

“…This suggests that the baryon, electric charge and strangeness carrying degree of freedom changes more rapidly across the transition in the stronger magnetic field. The higher peak and faster increasing around the transition temperature observed in the quadratic fluctuations of B, Q and S is consistent with the finding that the strength of transition becomes larger in a stronger magnetic field [20,81]. This may signal the approach to a possible critical end point in the phase diagram in the T -eB plane as suggested from Ref.…”

“…Eqs. [16][17][18][19][20][21], and for χ BQ 11 , we rather show χ BQ,f ree 11 /χ BQ 11 as χ BQ 11 = 0 in the ideal gas limit at eB = 0. One can clearly see that all the six ratios approach to 1 as √ eB/T grows at all four different temperatures, and the ratios increase faster at lower temperatures.…”

“…Based on lattice QCD studies it is well-known that a strong magnetic field can bring interesting effects on QCD thermodynamics [18], phase diagram [19,20], transport properties [8] as well as hadron spectroscopy [17,[21][22][23]. In particular the inverse magnetic catalysis with a reduction of chiral crossover transition temperature T pc in external magnetic fields [18,[24][25][26] have triggered a lot of interests [27][28][29][30][31][32][33][34][35][36][37][38][39][40].…”

QCD phase diagram in a constant magnetic background

“…After having discussed magnetic catalysis in low-energy models and theories of QCD, we next consider QCD lattice simulations. In the past decade, there have been a number of lattice calculations of QCD in a magnetic field [23][24][25][26][27]45,[68][69][70][71][72][73][74], which have improved our understanding of QCD in a magnetic background.…”

“…In Ref [73],. the authors find no sign of inverse catalysis in their N f = 3 simulations with a pion mass of 280 MeV.…”