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

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

Six-Photon Amplitudes

We present analytical results for all six-photon helicity amplitudes. For the computation of this loop induced process two recently developed methods, based on form factor decomposition and on multiple cuts, have been used. We obtain compact results, demonstrating the applicability of both methods to one-loop amplitudes relevant to precision collider phenomenology.Comment: replaced by published versio

Influence of strongly coupled, hidden scalars on Higgs signals

To investigate the possible effects of a light hidden sector on Higgs boson detection, we discuss a model of scalar singlets coupled to the Standard Model. The model effectively makes the Higgs width a free parameter due to additional invisible decay modes. This width can become arbitrarily large. Theoretical and experimental bounds on model parameters are presented. It is shown, how Standard Model predictions change and that in the case of large coupling, Higgs signals will be diluted. We study, to which extent such a strongly coupled, hidden sector can be excluded by present and future Higgs search experiments.Comment: 22 pages, Latex, 12 figures embedded with epsf.sty and epsfig.sty, to appear in Z. Phys.