Abstract
We investigate the behavior of the pseudocritical temperature of ${N}_{f}=2+1$ QCD as a function of a static magnetic background field for different values of the pion mass, going up to ${m}_{\ensuremath{\pi}}\ensuremath{\simeq}660\text{ }\text{ }\mathrm{MeV}$. The study is performed by lattice QCD simulations, adopting a stout staggered discretization of the theory on lattices with ${N}_{t}=6$ slices in the Euclidean temporal direction; for each value of the pion mass the temperature is changed moving along a line of constant physics. We find that the decrease of ${T}_{c}$ as a function of $B$, which is observed for physical quark masses, persists in the whole explored mass range, even if the relative variation of ${T}_{c}$ appears to be a decreasing function of ${m}_{\ensuremath{\pi}}$, approaching zero in the quenched limit. The location of ${T}_{c}$ is based on the renormalized quark condensate and its susceptibility; determinations based on the Polyakov loop lead to compatible results. On the contrary, inverse magnetic catalysis, i.e., the decrease of the quark condensate as a function of $B$ in some temperature range around ${T}_{c}$, is not observed when the pion mass is high enough. That supports the idea that inverse magnetic catalysis might be a secondary phenomenon, while the modifications induced by the magnetic background on the gauge field distribution and on the confining properties of the medium could play a primary role in the whole range of pion masses.
Highlights
The investigation of the properties of strong interactions in a magnetic background field has been the subject of numerous studies in the recent past, see, e.g., Refs. [1,2] for recent reviews
II we describe our lattice discretization of Nf 1⁄4 2 þ 1 QCD with a magnetic background, as well as the physical observables and the numerical setup to work on lines of constant physics
We have investigated the modification of the pseudocritical temperature of QCD with Nf 1⁄4 2 þ 1 flavors as a magnetic background field is switched on
Summary
The investigation of the properties of strong interactions in a magnetic background field has been the subject of numerous studies in the recent past, see, e.g., Refs. [1,2] for recent reviews. Lattice studies of Nf 1⁄4 2 QCD, adopting unimproved staggered fermions and larger-than-physical quark masses, showed a slightly increasing behavior of the pseudocritical temperature as a function of the magnetic field [12]. Many effects take place directly at the level of the confining properties of the theory [112,113,114,115,116,117,118], leading to anisotropies in the static quarkantiquark potential at T 1⁄4 0 and to a suppression of the string tension close to Tc [116] For this reason, one may ask whether the decrease of Tc could not be ascribed to these effects and be a sort of deconfinement catalysis, with the decrease of the quark condensate being just a secondary effect, induced by the fact that the magnetic background fosters deconfinement, chiral symmetry restoration.
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