Can a strong magnetic background modify the nature of the chiral   transition in QCD?
  The presence of a strong magnetic background can modify the nature and the dynamics of the chiral phase transition at finite temperature: for high enough magnetic fields, comparable to the ones expected to be created in noncentral high-energy heavy ion collisions at RHIC and the LHC, the original crossover is turned into a first-order transition. We illustrate this effect within the linear sigma model with quarks to one loop in the ${\rm MS}$ scheme for $N_{f}=2$. 
Eduardo S. Fraga and Ana J\'ulia Mizher