GLUON CONDENSATION IN NONPERTURBATIVE FLOW EQUATIONS

We employ nonperturbative flow equations for an investigation of the e ffective action in Yang-Mills theories. We compute the effective actio n Gamma[B] for constant color magnetic fields B and examine Savvidy's conjecture of an unstable perturbative vacuum. Our results indicate th at the absolute minimum of Gamma[B] occurs for B = 0. Gluon condensati on is described by a nonvanishing expectation value of the regularized composite operator Fmu nuFmu nu which agrees with phenomenological es timates. [S0556-2821(97)06024-4].