  Unambiguous isospin violation in the strong interaction sector is a key issue
in low energy hadronic physics, both experimentally and theoretically.
Bernstein has employed the Fermi-Watson theorem to demonstrate that pion
photoproduction is a process where isospin violation in the pi N system can be
revealed, an approach we review here. Here we propose a general operator
approach to the phenomenon in pion photoproduction, thereby providing an
analogue for the framework that was proposed for pi N scattering by Kaufmann
and Gibbs. The resulting set of amplitudes could form the basis for determining
the multipole amplitudes for photoproduction. Thus, the so resulting phase
shift determination from photoproduction can then be used via the Fermi-Watson
theorem to resolve discrepancies in pi N phase shift analyses. We point out
that casting effective Lagrangian results in terms of our framework would be
beneficial. The upcoming polarization experiments are an ideal setting to test
our approach, and also to constrain better the isotensor currents which
strictly are not forbidden.
