We propose a method to calculate scattering amplitudes using the
Bethe-Salpeter wave function inside the interaction range on the lattice. For
an exploratory study of this method, we evaluate a scattering length of I=2
S-wave two pions by the use of the on-shell scattering amplitude. Our result is
confirmed to be consistent with the value obtained from the conventional finite
volume method. The half-off-shell scattering amplitude is also evaluated.Comment: 5 pages, 4 figures; published versio
