AN EFFECTIVE ACTION FOR YANG-MILLS FIELD STRENGTHS

We investigate the gauge-invariant semi-classical effective action for the field strength tensor of Yang-Mills theories and emphasize that renormalization introduces a physical scale in this formulation. The stationary points of the renormalized action are partially classified by a topological number, and imply a non-vanishing 〈G2〉. For SU(2) all homogeneous vacuum solutions are explicitly constructed, for SU(3) numerical results are presented. The SU(2) and SU(3) ground states are found to differ qualitatively. An effective fermion theory is extracted which in the low-momentum regime reduces to a particular four-point interaction, but resembles gluon exchange at high momentum transfers. © 1990.