Instantons and spontaneous color symmetry breaking

The instanton interaction in QCD generates an effective potential for scalar quark–antiquark condensates in the color singlet and octet channels. For three light quark flavors the cubic term in this potential induces an octet condensate and may lead to “spontaneous breaking” of color in the vacuum. Realistic masses of the ρ- and η′-mesons are compatible with renormalization-group-improved instanton perturbation theory.