Light-Meson Two-Photon Decays in Full QCD
  We present a study of two-photon decays of light mesons, focusing on the neutral pion decay. This important process highlights the effects of the axial anomaly in QCD but has been little studied on the lattice. By applying the Lehmann-Symanzik-Zimmermann (LSZ) reduction formula, we reconstruct the electromagnetic matrix elements from three-point vector-vector Green functions calculated on 2+1-flavor isotropic clover lattices. 
Saul D. Cohen, Huey-Wen Lin, Jozef Dudek, Robert G. Edwards