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Threshold expansion of the sunset diagram

A. I. Davydychev, V. A. Smirnov

hep-pharXiv:hep-ph/9903328

Abstract

By use of the threshold expansion we develop an algorithm for analytical evaluation, within dimensional regularization, of arbitrary terms in the expansion of the (two-loop) sunset diagram with general masses m1, m2 and m3 near its threshold, i.e. in any given order in the difference between the external momentum squared and its threshold value, (m1+m2+m3)2. In particular, this algorithm includes an explicit recurrence procedure to analytically calculate sunset diagrams with arbitrary integer powers of propagators at the threshold.

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