Anomalous pseudoscalar-photon vertex in and out of equilibrium - art. no. 065002

The anomalous pseudoscalar-photon vertex is studied in real time in and out of equilibrium in a constituent quark model. The goal is to understand the in-medium modifications of this vertex, exploring the possibility of enhan ced isospin breaking by electromagnetic effects as well as the formation of neutral pion condensates in a rapid chiral phase transition in peripheral, ultrarelativistic heavy-ion collisions. In equilibrium the effective verte x is afflicted by infrared and pinch singularities that require hard therma l loop and width corrections of the quark propagator. The resummed effectiv e equilibrium vertex vanishes near the chiral transition in the chiral limi t. In a strongly our of equilibrium chiral phase transition we find that th e chiral condensate drastically modifies the quark propagators and the effe ctive vertex. The ensuing dynamics for the neutral pion results in a potent ial enhancement of isospin breaking and the formation of pi(0) condensates. While the anomaly equation and the axial Ward identity are not modified by the medium in or our of equilibrium, the effective real-time pseudoscalar- photon vertex is sensitive to low energy physics.