[en] We consider the infrared behaviour of tree-level QCD amplitudes at O(α_s²) and we discuss the factorization formulae relevant at this order by computing the new universal functions that control the singularities arising in the various soft and/or collinear limits

[en] I consider the singular behaviour of tree-level QCD amplitudes when the momenta of three partons become simultaneously parallel and I discuss the universal factorization formula that controls the singularities of the multiparton matrix elements in this collinear limit

[en] We consider QCD corrections to Higgs boson production through gluon-gluon fusion in hadron collisions. We compute the effects of soft-gluon emission to all orders. We present numerical results at the Tevatron and the LHC

[en] One-particle inclusive cross sections in the target fragmentation region are considered and an explicit calculation is performed in (φ³)₆ model field theory. The collinear divergences can be correctly absorbed into a parton density and a fragmentation function but the renormalized cross section gets a large logarithmic correction as expected in a two-scale regime. We find that the coefficient of such a correction is precisely the scalar DGLAP kernel. Furthermore, the consistency of this result with an extended factorization hypothesis is investigated. (orig.)

[en] We consider the transverse-momentum (q_T) distribution of Higgs bosons produced at hadron colliders. We use a formalism that uniformly treats both the small-q_T and large-q_T regions in QCD perturbation theory. At small q_T (q_T<< M_H, M_H being the mass of the Higgs boson), we implement an all-order resummation of logarithmically-enhanced contributions up to next-to-next-to-leading logarithmic accuracy. At large q_T (q_T > or approx. M_H), we use fixed-order perturbation theory up to next-to-leading order. The resummed and fixed-order approaches are consistently matched by avoiding double-counting in the intermediate-q_T region. In this region, the introduction of unjustified higher-order terms is avoided by imposing unitarity constraints, so that the integral of the q_T spectrum exactly reproduces the perturbative result for the total cross section up to next-to-next-to-leading order. Numerical results at the LHC are presented. These show that the main features of the q_T distribution are quite stable with respect to perturbative QCD uncertainties

[en] We discuss semi-inclusive deep inelastic scattering (DIS) in the z → 1 limit, in particular the relationship between fracture functions, generalised cut vertices and Green functions of the composite operators arising in the OPE. The implications, in the spin-polarised case, for testing whether the 'proton spin' effect is target-independent are explored. Explicit calculations in (f³)₆ theory are presented which are consistent with our observations

[en] We consider QCD corrections to Higgs boson production through gluon-gluon fusion in hadronic collisions. We discuss the effect of multiple soft-gluon emission to all orders in two observables: the total cross section gg->H and the transverse momentum distribution of the Higgs boson

[en] A simulation of the search for the Standard Model Higgs boson at the LHC, in the channel gg → H → WW →lν lν, is described. Higher-order QCD corrections are taken into account by using a reweighting procedure, which allows us to combine event rates obtained with the PYTHIA Monte Carlo program with the most up-to-date theoretical predictions for the transverse-momentum spectra of the Higgs signal and its corresponding WW background. With this method the discovery potential for Higgs masses between 140 and 180 GeV is recalculated and the potential statistical significance of this channel is found to increase considerably. For a Higgs mass of 165 GeV a signal-to-background ratio of almost 2:1 can be obtained. A statistical significance of five standard deviations might already be achieved with an integrated luminosity close to 0.4 fb^-1. Using this approach, an experimental effective K-factor of about 2.04 is obtained for the considered Higgs signature, which is only about 15% smaller than the theoretical inclusive K-factor. (author)

[en] We consider Standard Model Higgs boson production by gluon-gluon fusion in hadron collisions. We present a calculation of the next-to-next-to-leading order QCD corrections to the cross section in the H→WW→lνlν and H→ZZ→4l decay channels. The calculation is implemented in the parton level Monte Carlo program HNNLO and allows us to apply arbitrary cuts on the final state leptons and the associated jet activity. We present selected numerical results for the signal cross section at the LHC and the Tevatron, by using all the nominal cuts used in the Higgs boson search

[en] I present a calculation of the one particle deep inelastic cross section in the target fragmentation region in (φ³)₆. The renormalized cross section gets a large logarithmic correction whose coefficient is precisely the scalar DGLAP kernel. The result is found to be consistent with an extended factorization hypothesis and with infrared power counting. (orig.)