I am studying the Fujikawa method of determining the chiral anomalies in a $U(1)$ theory. As we know the basis vectors selected are the eigenstates of the Dirac operator. One of the reasons given is that the eigenstates diagonalize the action which is needed for determining an exact quantity such as Ward-Takahashi identities. Anyone care to explain? I am referring to *Path Integrals and Quantum Anomalies* by Kazuo Fujikawa and Hiroshi Suzuki.

This post imported from StackExchange Physics at 2014-06-29 09:36 (UCT), posted by SE-user SubhamDC