CHIRAL-SYMMETRY BREAKING IN D=3 NJL MODEL IN EXTERNAL GRAVITATIONAL AND MAGNETIC-FIELDS

The phase structure of the d = 3 Nambu-Jona-Lasinio model in curved sp acetime with a magnetic field is investigated in leading order of the 1/N expansion and in the linear curvature approximation (an external m agnetic field is treated exactly). The possibility of chiral symmetry breaking under the combined action of the external gravitational and m agnetic fields is shown explicitly. In some circumstances the chiral s ymmetry may a be restored due to the compensation of the magnetic fiel d by the gravitational field.