Interfering QCD/QED Vacuum Polarization
  Vacuum polarization mediated by quark loops is susceptible to external electromagnetic fields as well as to the QCD vacuum structure. Employing the stochastic vacuum model, we calculate the modification of the one-loop Euler-Heisenberg effective action due to stochastic color fields with the Fock-Schwinger technique. Our results indicate nonperturbative light quark contributions of the same order of magnitude as the usual QED terms. Various theoretical and experimental implications are discussed in this progress report. 
H.-Th. Elze, B. M\"uller and J. Rafelski