Recent news and results in the computation of NLO processes with new techniques

I illustrate new techniques and recently obtained results in the computation of perturbative QCD processes at the NLO accuracyComment: 6 pages, 2 figures, 3 tables, contribution to the proceedings of the 10th Hellenic School on Elementary Particle Physics and Gravity, Corfu 201

Two-loop off-shell QCD amplitudes in FDR

We link the FDR treatment of ultraviolet (UV) divergences to dimensional regularization up to two loops in QCD. This allows us to derive the one-loop and two-loop coupling constant and quark mass shifts necessary to translate infrared finite quantities computed in FDR to the MSbar renormalization scheme. As a by-product of our analysis, we solve a problem analogous to the breakdown of unitarity in the Four Dimensional Helicity (FDH) method beyond one loop. A fix to FDH is then presented that preserves the renormalizability properties of QCD without introducing evanescent quantities.Comment: 25 pages, 6 figure

FDR, an easier way to NNLO calculations: a two-loop case study

In this paper we illustrate the simplifications produced by FDR in NNLO computations. We show with an explicit example that - due to its four-dimensionality - FDR does not require an order-by-order renormalization and that, unlike the one-loop case, FDR and dimensional regularization (DR) generate intermediate two-loop results which are no longer linked by a simple subtraction of the ultraviolet (UV) poles in epsilon. Our case study is the two-loop amplitude for H -> gamma gamma, mediated by an infinitely heavy top loop, in the presence of gluonic corrections. We use this to elucidate how gauge invariance is preserved with no need of introducing counterterms in the Lagrangian. In addition, we discuss a possible four-dimensional approach to the infrared (IR) problem compatible with the FDR treatment of the UV infinities.Comment: 34 pages, 8 figures, version enlarged to be published in EPJ