The Large Hadron Collider (LHC) running actually at CERN, Geneva, is the most powerful man made high energy particle collider. It will enable us to observe or exclude the Standard Model Higgs boson, to clarify the nature of the electroweak symmetry breaking (EWSB) and to find possible signals of physics beyond the Standard Model (SM).Search for new physics signals at the CERN LHC frequently involves multi-particle final states, consisting of jets, leptons, photons and missing energy. Meaningful searches for these signatures require not only a very good knowledge of the expected signal, but also of all the SM backgrounds yielding identical final state signatures. Since leading-order calculations are affected by large uncertainties, next-to-leading (NLO) order corrections are necessary. For a long time, these corrections were available only for at most three final state particles. The current frontier of complexity are NLO calculations of 2 -> 4 reactions.The aim of this project is to carry out, on the one hand, several phenomenological studies of relevant processes for Higgs discovery and new physics searches at the LHC for 2 -> 4 processes at the one loop level. We will perform novel NLO QCD calculation of several multi-leg processes involving vector bosons and the top quark. On the other hand, we propose a novel technique to compute diboson production channels at approximated NNLO accuracy.The timeless and relevance of the project is given by the running of the LHC. We will release all the calculations as a Monte Carlo program to be used by the experimentalist to analyse data. The project will be performed at IFIC, a world leader centre for theoretical and experimental research in particle physics.