On the 1/Q correction to the C-parameter at two loops

Abstract

We provide an analytical calculation at the two loop level of the real non-abelian contribution to the leading (1/Q) correction to the mean value of the C parameter in e+e- annihilation, to complement the existing calculation of the abelian contribution; and we compare the result with the numerical `Milan factor' obtained using the soft approximation. We find agreement with the previous results. The use of the pinch technique to separate the various contributions yields insights into the structure of renormalon-type diagrams in a non-abelian theory.

Comments: 17 pages, 2 figures