The Complex-Mass Scheme and Unitarity in perturbative Quantum Field Theory

We investigate unitarity within the Complex-Mass Scheme, a convenient universal scheme for perturbative calculations involving unstable particles in Quantum Field Theory which guarantees exact gauge invariance. Since this scheme requires to introduce complex masses and complex couplings, the Cutkosky cutting rules, which express perturbative unitarity in theories of stable particles, are no longer valid. We derive corresponding rules for scalar theories with unstable particles based on Veltman's Largest-Time Equation and prove unitarity in this framework.Comment: 25 pages, PDFLaTeX, PDF figures, improved and slightly extended version appeared in European Physics Journal

Recola2: a one-loop matrix-element generator for BSM theories and SM effective field theory

We present the Recola2 library for the efficient generation and computation of one-loop amplitudes in Beyond-Standard-Model theories. Recola2 is based on Recola, an efficient one-loop amplitude generator for the Standard Model, and Rept1l, a newly developed tool to generate one-loop model files for Recola2 in a fully automated way. Recola2 is able to operate with non-trivial extensions of the SM, e.g. extended Higgs sectors and effective field theories. We discuss first applications to extended Higgs sectors and their renormalization.Comment: 6 pages, contribution to the proceedings of the 13th International Symposium on Radiative Corrections (RADCOR 2017

Recola2: REcursive Computation of One-Loop Amplitudes 2

We present the Fortran95 program Recola2 for the perturbative computation of next-to-leading-order transition amplitudes in the Standard Model of particle physics and extended Higgs sectors. New theories are implemented via model files in the 't Hooft-Feynman gauge in the conventional formulation of quantum field theory and in the Background-Field method. The present version includes model files for the Two-Higgs-Doublet Model and the Higgs-Singlet Extension of the Standard Model. We support standard renormalization schemes for the Standard Model as well as many commonly used renormalization schemes in extended Higgs sectors. Within these models the computation of next-to-leading-order polarized amplitudes and squared amplitudes, optionally summed over spin and colour, is fully automated for any process. Recola2 allows the computation of colour- and spin-correlated leading-order squared amplitudes that are needed in the dipole subtraction formalism. Recola2 is publicly available for download at http://recola.hepforge.org.Comment: 48 pages, 1 figure, matches published versio

NLO electroweak corrections in extended Higgs Sectors with RECOLA2

We present the computer code RECOLA2 along with the first NLO electroweak corrections to Higgs production in vector-boson fusion and updated results for Higgs strahlung in the Two-Higgs-Doublet Model and Higgs-Singlet extension of the Standard Model. A fully automated procedure for the generation of tree-level and one-loop matrix elements in general models, including renormalization, is presented. We discuss the application of the Background-Field Method to the extended models. Numerical results for NLO electroweak cross sections are presented for different renormalization schemes in the Two-Higgs-Doublet Model and the Higgs-Singlet extension of the Standard Model. Finally, we present distributions for the production of a heavy Higgs boson.Comment: 47 pages, 29 figures, pdflatex, version to appear in JHE

Anomalous triple-gauge-boson interactions in vector-boson pair production with RECOLA2

Diboson production at the LHC is a process of great importance both in the context of tests of the SM and for direct searches for new physics. In this paper we present a phenomenological study of WW, WZ, and ZZ production considering event selections of interest for the anomalous triple-gauge-boson-coupling searches at the LHC: we provide theoretical predictions within the Standard Model at NLO QCD and NLO EW accuracy and study the effect of the anomalous triple-gauge-boson interactions at NLO QCD. For WW and ZZ production, the contribution of the gluon-initiated loop-induced processes is included. Anomalous triple-gauge-boson interactions are parametrized in the EFT framework. This paper is the first application of RECOLA2 in the EFT context.Comment: 36 pages, 56 pdf figures, latex. Corrected typo in Eq.(3.2). One reference added. Published versio

Dependent Lindeberg central limit theorem and some applications

In this paper, a very useful lemma (in two versions) is proved: it simplifies notably the essential step to establish a Lindeberg central limit theorem for dependent processes. Then, applying this lemma to weakly dependent processes introduced in Doukhan and Louhichi (1999), a new central limit theorem is obtained for sample mean or kernel density estimator. Moreover, by using the subsampling, extensions under weaker assumptions of these central limit theorems are provided. All the usual causal or non causal time series: Gaussian, associated, linear, ARCH($\infty$), bilinear, Volterra processes,$...$, enter this frame

NLO QCD and EW corrections to processes involving off-shell top quarks

We review recent results on next-to-leading order (NLO) QCD and electroweak (EW) corrections for processes involving off-shell top quarks. For the off-shell production of two top quarks that decay leptonically, the full NLO EW corrections have been computed. For the very same process in association with a Higgs boson, EW corrections have been calculated and combined with existing NLO QCD corrections. In both cases, selected differential distributions are shown. In these proceedings, particular emphasis is put on the effect of the EW corrections as well as the off-shell contributions.Comment: 6 pages, 6 figures. Contribution to the proceedings of the 13th International Symposium on Radiative Corrections (RADCOR 2017

Full NLO QCD corrections to off-shell tt‾bb‾t\overline{t}b\overline{b} production

In this article, we report on the computation of the next-to-leading order (NLO) QCD corrections to pp→μ−¯νμe+νe¯bb¯bb at the LHC, which is an irreducible background to pp→t¯tH(→b¯b). This is the first time that a full NLO computation for a 2→8 process with 6 external strongly interacting partons is made public. No approximations are used, and all off-shell and interference effects are taken into account. Cross sections and differential distributions from the full computation are compared to results obtained by using a double-pole approximation for the top quarks. The difference between the full calculation and the one using the double-pole approximation is in general below 5% but can reach 10% in some regions of phase space