Chiral transition in a strong magnetic background

The presence of a strong magnetic background can modify the nature and the dynamics of the chiral phase transition at finite temperature. We compute the modified effective potential in the linear sigma model with quarks to one loop in the MS scheme for N-f=2. For fields eB similar to 5m(pi)(2) and larger a crossover is turned into a weak first-order transition. We discuss possible implications for noncentral heavy ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider and for the primordial QCD transition.