QCD phase diagram in a magnetic background for different values of the pion mass

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(pi) similar or equal to 660 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(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.