DYNAMICAL BREAKDOWN OF SYMMETRY IN QUADRATIC QUANTUM-GRAVITY

In the ladder approximation, the effective potential for composite fer mion fields and Schwinger-Dyson equations are explicitly obtained in R -2 gravity against a flat background. The two-dimensional case is cons idered in the covariant and conformal gauges, while the four-dimension al case is treated in the covariant gauge, which ensures the absence o f nonminimal terms in the graviton propagator. A detailed numerical an alysis of nonlinear integral equations for structure functions that de termine the exact fermion propagator is performed. The dynamical fermi on mass is found as a function of the coupling constant. It is shown t hat, in all gauges considered in this study, there exists a phase tran sition accompanied by the breakdown of chiral symmetry and by the dyna mical generation of a fermion mass.