Gauge discrepancies in calculations of (γ, 2e) on helium

We have studied the dependency and sensitivity of the triple differential cross section (TDCS) for (γ, 2e) on He with respect to the gauge formulation that one employs to represent the TDCS. This analysis has been performed using a variety of analytic initial- and final-state wavefunctions. It was found that the TDCS is very sensitive to the representation of the final-state wavefunction in all geometries and all formulations of the TDCS. When the detected electrons are of unequal energy the TDCS is also sensitive to the initial-state wavefunction. The predictions using all combinations of initial- and final-channel wavefunctions are gauge dependent and vary enormously in absolute size. (author)