Perturbative thresholds in the physical region

Abstract

We consider unstable-particle scattering in the context of 3-body processes. We show that all partial-wave cross-sections are finite and positive, and the total cross-section is proportional to the transverse size of space in the region of on-shell particle exchange. We comment on the role of loop corrections.

Comments: 13 + 1 pages, plain LaTeX 2e + PostScript, to appear in Z. Phys. C