Zero-threshold expansion of two-loop self-energy diagrams

Abstract

An algorithm is constructed to derive a small momentum expansion for two-loop two-point diagrams in all cases where, due to the presence of physical thresholds, there are singularities at zero external momentum. The coefficients of this ``zero-threshold'' expansion are calculated analytically for arbitrary masses. Numerical examples, using diagrams occurring in the Standard Model, illustrate the convergence of the expansion below the first non-zero threshold.

Comments: 24 pages latex with 17 postscript figures. A complete postscript file is available by anonymous ftp from 129.177.40.57 [anonymous.davydychev]leiden15-94.ps. Leiden/Durham preprint INLO-PUB-15/94, DTP-94/86