pi_0 --> gamma gamma and the axial anomaly at non zero temperature

Abstract

In vacuum, in the chiral limit the coupling of a pion to two on-shell photons is directly related to the coefficient of the axial anomaly in QED. This relationship is lost at any nonzero temperature. Explicit calculations show that the coupling decreases with temperature and vanishes at Tc, the temperature of chiral symmetry restoration.

Comments: 4 pages, latex, 2 figs using epsfig. Contribution to the 31st Rencontres de Moriond, "QCD and High Energy Hadronic Interactions", March 97