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

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.Comment: 17 pages, 2 figure

Azimuthal correlation in DIS

We introduce the azimuthal correlation for the deep inelastic scattering process. We present the QCD prediction to the level of next-to-leading log resummation, matching to the fixed order prediction. We also estimate the leading non-perturbative power correction. The observable is compared with the energy-energy correlation in e+e- annihilation, on which it is modelled. The effects of the resummation and of the leading power correction are both quite large. It would therefore be particularly instructive to study this observable experimentally.Comment: 33 pages, 4 figures, JHEP class included. One figure and some clarifications adde