NAMBU-JONA-LASINIO MODEL IN CURVED SPACETIME WITH MAGNETIC-FIELD

We discuss the phase structure of the NJL model in curved spacetime wi th magnetic field using 1/N-expansion and linear curvature approximati on. The effective potential for composite fields <(psi)over bar psi> i s calculated using the proper-time cutoff in the following cases: (a) at nonzero curvature, (b) at nonzero curvature and nonzero magnetic fi eld, and (c) at nonzero curvature and nonzero covariantly constant gau ge field. Chiral symmetry breaking is studied numerically. We show tha t the gravitational field may compensate the effect of the magnetic fi eld what leads to restoration of chiral symmetry.