Gluon Condensation in Nonperturbative Flow Equations

We employ nonperturbative flow equations for an investigation of the effective action in Yang-Mills theories. We compute the effective action Γ[B] for constant color magnetic fields B and examine Savvidy’s conjecture of an unstable perturbative vacuum. Our results indicate that the absolute minimum of Γ[B] occurs for B = 0. Gluon condensation is described by a nonvanishing expectation value of the regularized composite operator FμνF μν which agrees with phenomenological estimates.