THE CONTRIBUTION OF AXIAL-ANOMALY TRIANGLE DIAGRAMS FOR THE PI(0)-]2-GAMMA PROCESS IN COSMOLOGY

By means of the real time Green's function method, the decay width of the pi(0)-->2 gamma process through axial anomaly triangle diagram at finite temperature and finite density is calculated and its effect on the evolution of the universe is discussed. We have found that the dec ay width increases with temperature but decreases with the density. At the beginning of the lepton era, the decay width almost increases to six times the decay width at zero temperature. A critical density at w hich the decay width becomes zero is given. The contribution of axial anomaly to the cosmic background gamma-radiation is considered.