Compton scattering by pion: there is no room for the off-shell effects

Abstract

We show that the off-shell contributions in Compton scattering by pion may exist only in the single exchange diagrams. These contributions are canceled completely in the total gauge-invariant amplitude as it confirmed by one-loop calculations. It explains, in particular, some results of the chiral pertubation theory in the order $p^4$ but this cancelation has no relation to chiral symmetry.

11 pages, LaTeX2e, 4 figures included