  An investigation of the Nambu-Jona-Lasinio model with external constant
electromagnetic and weak gravitational fields is carried out in three- and
four-dimensional spacetimes. The effective potential of the composite
bifermionic fields is calculated keeping terms linear in the curvature, while
the electromagnetic field effect is treated exactly by means of the proper-time
formalism. Numerical simulations of the dynamical symmetry breaking phenomenon
accompanied by some phase transitions are presented.
