Phase structure of the QCD vacuum in a magnetic field at low temperature

We study the QCD phase structure in magnetic field H at low temperature T. The hadronic phase free energy in a constant homogeneous magnetic field is calculated in one-loop approximation of the chiral perturbation theory. The dependence of the quark and gluon condensates upon the temperature and field strength is found. It is shown that the chiral phase transition order parameter 〈q̄q〉 remains constant provided field strength and temperature are related via H=const.·T2.