$\pi^0$ to two-photon decay in lattice QCD

$\pi^0\rightarrow\gamma\gamma$ decay, which is induced by the axial anomaly. Using the overlap fermion we explicitly calculate the amplitude for the $\pi^0 \rightarrow\gamma^*\gamma^*$ process. Our result nicely reproduces the prediction from the axial anomaly in the on-shell limit thanks to the exact chiral symmetry on the lattice, and also give a useful information for the lattice calculation of hadronic light-by-light scattering diagram for muon g-2.