159 research outputs found
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
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