QCD effective lagrangian and condensation of chromomagnetic flux tubes

Abstract We compute the effective action for covariantly constant gauge fields that are solutions of the sourceless Yang–Mills equation and have the form of magnetic flux tubes. They represent a superposition of infinite many alternating monopole/anti-monopole pairs situated at infinity, with each pair having a structure similar to the Nielsen–Olesen magnetic flux tube. The chromomagnetic flux tubes condensation is stable and indicates that the Yang–Mills vacuum state is highly degenerate.