Quantum chromodynamics in hadron collider experiments: towards automated one-loop calculations for multi-particle processes. Application to the production of 2 photons and 1 jet

The future CERN collider (LHC) has a fantastic potential of discovery, provided quantum chromodynamics can be quantitatively predicted. To do so, it is necessary to work at NLO approximation in order to reduce the dependence of the -cross-section on- the non-physical scales. To obtain results in this approximation, one has to calculate the cross-sections of the partonic subprocesses contributing to the studied reaction at the lowest order, and also the virtual corrections (loop corrections) and the real corrections. The calculation of the virtual corrections remains very complicated if the number of external particles is greater than four or if the external (internal) particles are massive. in this thesis, an automatic method which enables to calculate one loop diagrams with five external legs and which can be generalized to the case of massive particles is presented. In a first part, we describe different tools and methods necessary to such calculations. We then apply -them to the calculation of the gg →γγ g reaction, which interests the ATLAS and CMS experimentalists as the background for the Higgs boson search. We also give the explicit result for this amplitude for each helicity configuration in a compact form and a clearly gauge invariant representation. We finally present a phenomenological study of this reaction. (author)