Recent Theoretical Developments in LEP 2 Physics

Recent theoretical developments in electron-positron annihilation into fermion pairs are summarized. In particular, two-fermion production, DPA for WW signal, single-W production and ZZ signalComment: 6 pages(Latex), 4 figures. To appear in Proceedings of ICHEP2000, Osaka, Japan, 27 July - 2 August 200

Non-Annihilation Processes, Fermion-Loop and QED Radiation

The bulk of large radiative corrections to any process can be obtained by promoting coupling constants to be running ones and by including QED radiation at the leading logarithmic level via structure functions evoluted at some scale. The problem of fixing the proper scale in running coupling constants and in structure functions for non-annihilation processes is briefly addressed and the general solution is analyzed.Comment: 9 pages(Latex), 9 figures. Presented at the 5th International Symposium on Radiative Corrections (RADCOR--2000) Carmel CA, USA, 11--15 September, 200

The Twofold Way, a Short Disquisition of LEP Physics

A condensed survey of various aspects of LEP 1 physics is presented with a critical examination of the ingredients that are available for theoretical predictions. A prototype of comparisons for 2f calculations can be found in hep-ph/9902452.Comment: 16 pages(Latex). To appear in the Proceedings of "XIVth International Workshop: High Energy Physics and Quantum Field Theory (QFTHEP99)", Moscow, Russia, 27 May - 2 June 199

Two-Loop Threshold Singularities, Unstable Particles and Complex Masses

The effect of threshold singularities induced by unstable particles on two-loop observables is investigated and it is shown how to cure them working in the complex-mass scheme. The impact on radiative corrections around thresholds is thoroughly analyzed and shown to be relevant for two selected LHC and ILC applications: Higgs production via gluon fusion and decay into two photons at two loops in the Standard Model. Concerning Higgs production, it is essential to understand possible sources of large corrections in addition to the well-known QCD effects. It is shown that NLO electroweak corrections can incongruently reach a 10 % level around the WW vector-boson threshold without a complete implementation of the complex-mass scheme in the two-loop calculation.Comment: LaTeX, 12 pages, 7 figure

NNLO Computational Techniques: the Cases H -> gamma gamma and H -> g g

A large set of techniques needed to compute decay rates at the two-loop level are derived and systematized. The main emphasis of the paper is on the two Standard Model decays H -> gamma gamma and H -> g g. The techniques, however, have a much wider range of application: they give practical examples of general rules for two-loop renormalization; they introduce simple recipes for handling internal unstable particles in two-loop processes; they illustrate simple procedures for the extraction of collinear logarithms from the amplitude. The latter is particularly relevant to show cancellations, e.g. cancellation of collinear divergencies. Furthermore, the paper deals with the proper treatment of non-enhanced two-loop QCD and electroweak contributions to different physical (pseudo-)observables, showing how they can be transformed in a way that allows for a stable numerical integration. Numerical results for the two-loop percentage corrections to H -> gamma gamma, g g are presented and discussed. When applied to the process pp -> gg + X -> H + X, the results show that the electroweak scaling factor for the cross section is between -4 % and + 6 % in the range 100 GeV < Mh < 500 GeV, without incongruent large effects around the physical electroweak thresholds, thereby showing that only a complete implementation of the computational scheme keeps two-loop corrections under control.Comment: LaTeX, 70 pages, 8 eps figure

Higgs boson couplings: Measurements and theoretical interpretation

This report will review the Higgs boson properties: the mass, the total width and the couplings to fermions and bosons. The measurements have been performed with the data collected in 2011 and 2012 at the LHC accelerator at CERN by the ATLAS and CMS experiments. Theoretical frameworks to search for new physics are also introduced and discussed.Comment: 67 pages, 23 figure