Four-fermion interaction model in a constant magnetic field at finite temperature and chemical potential

We investigate the influence of an external magnetic field on chiral symmetry breaking in a four-fermion interaction model at finite temperature and chemical potential. Using the Fock-Schwinger proper time method, we calculate the effective potential for the four-fermion interaction model to leading order in the 1/N-c, expansion. The phase structure of the chiral symmetry breaking is determined in the T-mu, H-T and mu-H planes. The external magnetic field modifies the phase structure. It is found that a new phase appears for a large chemical potential.