Electromagnetic Fields in the QCD Vacuum

Quarks play an active role in shaping the QCD vacuum structure. Being dual carriers of both color' and electric’ charges they also respond to externally applied electromagnetic fields. Thus, in principle, the vacuum of strong interactions influences higher order QED processes such as photon-photon scattering. We survey here the current status of the understanding of the vacuum structure of strong interactions, and take a fresh look at its electromagnetic properties.