CP violation and chiral symmetry restoration in the hot linear sigma   model in a strong magnetic background
  We study the effects of CP violation on the nature of the chiral transition within the linear sigma model with two flavors of quarks. The finite-temperature effective potential containing contributions from nontrivial values for the parameter $\theta$ is computed to one loop order and their minima structure is analyzed. Motivated by the possibility of observing the formation of CP-odd domains in high-energy heavy ion collisions, we also investigate the behavior of the effective potential in the presence of a strong magnetic background. We find that the nature of the chiral transition is influenced by both $\theta$ and the magnetic field. 
Ana J\'ulia Mizher and Eduardo S. Fraga