Kay Schönwald

A bstract: We consider the photon-energy spectrum of the inclusive radiative decay B → X _s γ , induced by the electromagnetic dipole operator O ₇ , to next-to-next-to-next-to-leading order and calculate the complete corrections for light fermions, for the contributions with two closed massive fermion loops, and for the limit of large QCD colour factors N _c in the remaining part. We discuss the integrated decay rate both without and with a cut on the photon energy. In addition to the on-shell renormalization of the bottom-quark mass, we also consider the kinetic mass and the MSR mass schemes. The latter two lead to an improved perturbative behaviour of the decay rate.

A bstract: We compute the complete top-quark-induced next-to-leading order electroweak corrections to the form factors entering gluon-induced Higgs boson pair production. We consider the top quark contribution in the limit where the Mandelstam variables are much larger than all other scales involved in the process and compute about a hundred expansion terms in analytic form. They are used to obtain precise numerical results even for fairly low values of the transverse momentum of the Higgs boson. We show that these electroweak corrections at high energies are of the order of −10%. We also discuss the leading logarithmic corrections of the analytic expressions.

A bstract: We implement the recently-calculated analytic expressions for the next-to-leading order QCD corrections to gg → ZH in ggxy. This provides a flexible framework for investigating partonic and hadronic cross sections for various top quark mass renormalization schemes. We augment the Z boson with leptonic decays, including spin correlations and off-shell effects, and furthermore provide an interface to POWHEG. This enables simulations with parton showers, performed using Pythia.

A bstract: We compute two-loop corrections to the associated production of a Higgs boson with a Z boson and to off-shell Z boson pair production in the gluon fusion channel, mediated by a heavy quark. We perform deep expansions in the high-energy region and around the forward limit and show that their combination covers the whole phase space. Our results constitute the next-to-leading order virtual corrections to these processes. Their numerical evaluation is fast and the dependence on all parameters is maintained, thus a change of parameter values or renormalization scheme is straightforward. As a by-product of our calculation, we also obtain the two-loop heavy quark mediated virtual corrections to the processes of off-shell di-photon and photon- Z production.

A bstract: We compute three-loop virtual corrections to the associated production of a Higgs boson with a Z boson in the large- m _t limit. We describe in detail the application of the asymptotic expansion and provide, for all form factors, analytic results for the first three terms in the 1/ m _t expansion. We also provide numerical routines implemented in the C++ library ggxy.