Towards LHC phenomenology at the loop level: A new method for one-loop amplitudes

A precise understanding of LHC phenomenology requires the inclusion of one-loop corrections for multi-particle final states. In this talk we describe a semi-numerical method to compute one-loop amplitudes with many external particles and present first applications.Comment: 5 pages latex, 1 ps fig., 1 eps fig., Conference Proceedings Radcor 200

Multiparticle amplitudes at one-loop: an algebraic/numeric approach

We discuss algebraic/numeric methods to compute one-loop corrections for multiparticle/jet production cross sections. By using efficient reduction algorithms a compact expression for the ggg\gamma\gamma -> 0 amplitude is obtained. Further a numerical approach for 6-point 1-loop diagrams is presented.Comment: 5 pages, Talk given at the 7th DESY Workshop On Elementary Particle Theory: Loops And Legs In Quantum Field Theory, Zinnowitz, Germany, 25-30 Apr 200

New one-loop techniques and first applications to LHC phenomenology

In this talk we describe our approach for the computation of multi-leg one-loop amplitudes and present some first results relevant for LHC phenomenology.Comment: 5 pages, to appear in the proceedings of the conference "Loops and Legs", Eisenach, 200

Nonperturbative three-point functions of the O(N) sigma model in the 1/N expansion at NLO

We present a calculation of the three-point functions of the O(N)-symmetric sigma model. The calculation is done nonperturbatively by means of a higher-order 1/N expansion combined with a tachyonic regularization which we proposed in previous publications. We use the results for calculating the standard model process ff -> H -> WW nonperturbatively in the quartic coupling of the scalar sector

Loops and legs beyond perturbation theory

Within the non-perturbative 1/N expansion, we discuss numerical methods for calculating multi-loop Feynman graph needed to derive physical scattering amplitudes. We apply higher order 1/N methods to the scalar sector of the standard model, and show the existence of a mass saturation effect. The mass saturation has direct implications for future searches at the LHC and at possible muon colliders.Comment: Talk presented at the Loops and Legs in Quantum Field Theory 2000 meetin

Muon colliders and the non-perturbative dynamics of the Higgs boson

A muon collider operating in the TeV energy range can be an ideal s-channel Higgs boson factory. This is especially true for a heavy Higgs boson. The non-perturbative dynamical aspects of such a Higgs boson were recently investigated with large N expansion methods at next to leading order, and reveal the existence of a mass saturation effect. Even at strong coupling, the Higgs resonance remains always below 1 TeV. However, if the coupling is strong enough, the resonance becomes impossible to be detected.Comment: Contributed to the International Conference on Physics Potential and Development of mumu Colliders, December 15-17, 1999, San Francisco, C

A numerical approach to infrared divergent multi-parton phase space integrals

It is described how the method of sector decomposition can serve to disentangle overlapping infrared singularities, in particular those occurring in the calculation of the real emission part of e+e- to 2 jets and e+e- to 3 jets at NNLO.Comment: 5 pages, contribution to the proceedings of the conference "Loops and Legs in Quantum Field Theory", Zinnowitz, Germany, April 25-30, 200

Radiative corrections in a minimal extension of the standard model

Radiative corrections are studied within an extension of the standard model, containing extra singlet scalars. The calculations determine the effect of a large width of the Higgs boson on radiative corrections. They throw some light on the treatment of unstable particles inside loop-graphs.Comment: 5 pages, LaTeX, 1 eps-figur