578 research outputs found
Multiloop Integrand Reduction for Dimensionally Regulated Amplitudes
We present the integrand reduction via multivariate polynomial division as a
natural technique to encode the unitarity conditions of Feynman amplitudes. We
derive a recursive formula for the integrand reduction, valid for arbitrary
dimensionally regulated loop integrals with any number of loops and external
legs, which can be used to obtain the decomposition of any integrand
analytically with a finite number of algebraic operations. The general results
are illustrated by applications to two-loop Feynman diagrams in QED and QCD,
showing that the proposed reduction algorithm can also be seamlessly applied to
integrands with denominators appearing with arbitrary powers.Comment: Published version. 5 pages, 2 figure
FormCalc 8: Better Algebra and Vectorization
We present Version 8 of the Feynman-diagram calculator FormCalc. New features
include in particular significantly improved algebraic simplification as well
as vectorization of the generated code. The Cuba Library, used in FormCalc,
features checkpointing to disk for all integration algorithms.Comment: 7 pages, LaTeX, proceedings contribution to ACAT 2013, Beijing,
China, 16-21 May 201
The Integrand Reduction of One- and Two-Loop Scattering Amplitudes
The integrand-level methods for the reduction of scattering amplitudes are
well-established techniques, which have already proven their effectiveness in
several applications at one-loop. In addition to the automation and refinement
of tools for one-loop calculations, during the past year we observed very
interesting progress in developing new techniques for amplitudes at two- and
higher-loops, based on similar principles. In this presentation, we review the
main features of integrand-level approaches with a particular focus on
algebraic techniques, such as Laurent series expansion which we used to improve
the one-loop reduction, and multivariate polynomial division which unveils the
structure of multi-loop amplitudes.Comment: 7 pages, v2: fixed typos, added references. Presented at "Loops and
Legs in Quantum Field Theory", Wernigerode, Germany, 15-20 April 201
FormCalc 7
We present additions and improvements in Version 7 of FormCalc, most notably
analytic tensor reduction, choice of OPP methods, and MSSM initialization via
FeynHiggs, as well as a parallelized Cuba library for numerical integration.Comment: 6 pages, proceedings contribution to ACAT 2011, Uxbridge, London,
September 5-9, 201
NLO QCD corrections to the production of Higgs plus two jets at the LHC
We present the calculation of the NLO QCD corrections to the associated
production of a Higgs boson and two jets, in the infinite top-mass limit. We
discuss the technical details of the computation and we show the numerical
impact of the radiative corrections on several observables at the LHC. The
results are obtained by using a fully automated framework for fixed order NLO
QCD calculations based on the interplay of the packages GoSam and Sherpa. The
evaluation of the virtual corrections constitutes an application of the
d-dimensional integrand-level reduction to theories with higher dimensional
operators. We also present first results for the one-loop matrix elements of
the partonic processes with a quark-pair in the final state, which enter the
hadronic production of a Higgs boson together with three jets in the infinite
top-mass approximation.Comment: 9 pages, 7 figures, references added, published in Phys.Lett.
Hereditary inclusion-body myopathy with sparing of the quadriceps: the many tiles of an incomplete puzzle
The hereditary inclusion-body myopathies encompass several syndromes with autosomal recessive or dominant inheritance. Despite a different clinical presentation they all have a progressive course leading to severe disability and share similar pathologic findings at the muscle biopsy. Quadriceps-sparing autosomal recessive hereditary inclusion-body myopathy (h-IBM) is the commonest form and is tied to mutations of the UDP-Nacetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) that codes for a rate-limiting enzyme in the sialic acid biosynthetic pathway. Despite the identification of the causative gene defect, it has not been clarified how mutations of the GNE gene impair muscle homeostasis. Although several lines of evidence argue in favor of an abnormal sialylation of muscle glycoproteins playing a key role in h-IBM pathogenesis, others studies have demonstrated new functions of the GNE gene, outside the sialic acid biosynthetic pathway, that may also be relevant. This review illustrates the clinical and pathologic characteristics of h- IBM and the main clues available to date concerning the possible pathogenic mechanisms of this disorder. Understanding the molecular mechanism underlying h-IBM pathology is a fundamental requisite to plan a future attempt to therapy
A complete one-loop calculation of electroweak supersymmetric effects in -channel single top production at LHC
We have computed the complete one-loop electroweak effects in the MSSM for
single top (and single antitop) production in the -channel at hadron
colliders, generalizing a previous analysis performed for the dominant
final state and fully including QED effects. The results are quite similar for
all processes. The overall Standard Model one-loop effect is small, of the few
percent size. This is due to a compensation of weak and QED contributions that
are of opposite sign. The genuine SUSY contribution is generally quite modest
in the mSUGRA scenario. The experimental observables would therefore only
practically depend, in this framework, on the CKM coupling.Comment: 25 pages, several eps figures. Update corresponding to published
versio
Automated one-loop calculations with GoSam 2.0
We present the version 2.0 of the program GoSam, which is a public program
package to compute one-loop corrections to multi-particle processes. The
extended version of the "Binoth-Les-Houches-Accord" interface to Monte Carlo
programs is also implemented. This allows a large flexibility regarding the
combination of the code with various Monte Carlo programs to produce fully
differential NLO results, including the possibility of parton showering and
hadronisation. We describe the new features of the code and illustrate the wide
range of applicability for multi-particle processes at NLO, both within and
beyond the Standard Model.Comment: 9 pages, talk given at the conference "Loops and Legs in Quantum
Field Theory", Weimar, Germany, April 201
GoSam-2.0: a tool for automated one-loop calculations within the Standard Model and beyond
We present the version 2.0 of the program package GoSam for the automated
calculation of one-loop amplitudes. GoSam is devised to compute one-loop QCD
and/or electroweak corrections to multi-particle processes within and beyond
the Standard Model. The new code contains improvements in the generation and in
the reduction of the amplitudes, performs better in computing time and
numerical accuracy, and has an extended range of applicability. The extended
version of the "Binoth-Les-Houches-Accord" interface to Monte Carlo programs is
also implemented. We give a detailed description of installation and usage of
the code, and illustrate the new features in dedicated examples.Comment: replaced by published version and reference adde
Hadronic production of bottom-squark pairs with electroweak contributions
We present the complete computation of the tree-level and the next-to-leading
order electroweak contributions to bottom-squark pair production at the LHC.
The computation is performed within the minimal supersymmetric extension of the
Standard Model. We discuss the numerical impact of these contributions in
several supersymmetric scenarios.Comment: 33 pages, v2: preprint numbers correcte
- …