432 research outputs found
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particles, are no longer valid.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(), 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 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
Effects of anomalous triple-gauge-boson interactions in diboson production with RECOLA2
Diboson production processes are of great importance in high-energy physics
and a precise theoretical knowledge of VV production is mandatory not only in
view of precision tests of the Standard Model but also in the one of new
physics searches. We present results of arXiv:1804.01477, where we computed the
NLO QCD and NLO electroweak corrections to diboson production processes at the
LHC including the effect of the anomalous triple-gauge-boson interactions at
NLO QCD accuracy. The anomalous triple-gauge-boson interactions are
parametrized in terms of higher-dimensional operators in the effective field
theory framework. Our calculation is the first application of Recola2 to
effective field theory models.Comment: Talk presented at Loops and Legs in Quantum Field Theory (LL2018), 29
April 2018 - 04 May 2018, St. Goar, Germany. Submitted to PoS. arXiv admin
note: text overlap with arXiv:1807.1019
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