HQET quark-gluon vertex at one loop

We calculate the HQET quark-gluon vertex at one loop, for arbitrary external momenta, in an arbitrary covariant gauge and space-time dimension. Relevant results and algorithms for the three-point HQET integrals are presented. We also show how one can obtain the HQET limit directly from QCD results for the quark-gluon vertex.Comment: LaTeX2e, 22 pages, 8 figures (eps files), REDUCE program is available at http://wwwthep.physik.uni-mainz.de/Publications/progdata/mzth0101

Threshold and pseudothreshold values of the sunset diagram

Analytic results for the threshold and pseudothreshold values of the sunset diagram with arbitrary masses are obtained in terms of dilogarithms of ratios of the masses.Comment: 11 pages, plain LaTe

Small-threshold behaviour of two-loop self-energy diagrams: two-particle thresholds

The behaviour of two-loop two-point diagrams at non-zero thresholds corresponding to two-particle cuts is analyzed. The masses involved in a cut and the external momentum are assumed to be small as compared to some of the other masses of the diagram. By employing general formulae of asymptotic expansions of Feynman diagrams in momenta and masses, we construct an algorithm to derive analytic approximations to the diagrams. In such a way, we calculate several first coefficients of the expansion. Since no conditions on relative values of the small masses and the external momentum are imposed, the threshold irregularities are described analytically. Numerical examples, using diagrams occurring in the Standard Model, illustrate the convergence of the expansion below the first large threshold.Comment: 28 pages (including 23 pages of text in latex and 5 pages with 6 figures in a separate postcript file

Hadronic Corrections at O(alpha^2) to the Energy Spectrum of Muon Decay

We consider the impact of O(alpha^2) hadronic corrections to the energy spectrum of the decay electron in muon decay. We find that the correction can be described, within good approximation, by a linear function in the electron energy. Explicit expressions for the form factors needed in an approach based on dispersion integrals are given.Comment: 12 pages Latex with 4 figure