FLOW EQUATIONS AND BRS INVARIANCE FOR YANG-MILLS THEORIES

Flow equations describe the evolution of the effective action GAMMA(k) in the process of varying an infrared cutoff k. The presence of the i nfrared cutoff explicitly breaks gauge and hence BRS invariance. We de rive modified Slavnov-Taylor identities, which are valid for nonvanish ing k. They guarantee the BRS invariance of GAMMA(k) for k --> 0, and hence allow the study of non-abelian gauge theories by integrating the flow equations. Within a perturbative expansion of GAMMA(k), we deriv e an equation for a k dependent mass term for the gauge fields implied by the modified Slavnov-Taylor identities.