Electromagnetic triangle anomaly and neutral pion condensation in QCD vacuum

摘要

We study the QCD vacuum structure under the influence of an electromagnetic field with a nonzero second Lorentz invariant I-2 = E . B. We show that the presence of I-2 can induce neutral pion (pi(0)) condensation in the QCD vacuum through the electromagnetic triangle anomaly. Within the frameworks of chiral perturbation theory at leading small-momenta expansion as well as the Nambu-Jona-Lasinio model at leading 1/N-c expansion, we quantify the dependence of the pi(0) condensate on I-2. The stability of the pi(0)-condensed vacuum against the Schwinger charged pair production due to electric field is also discussed. (C) 2016 The Authors. Published by Elsevier B.V.