Recola2: REcursive Computation of One-Loop Amplitudes 2
TL;DR: The Fortran95 program Recola2 is presented, for the perturbative computation of next-to-leading-order transition amplitudes in the Standard Model of particle physics and extended Higgs sectors, and allows the computation of colour- and spin-correlated leading-order squared amplitudes that are needed in the dipole subtraction formalism.
About: This article is published in Computer Physics Communications.The article was published on 2017-05-01 and is currently open access. It has received 236 citations till now. The article focuses on the topics: Feynman diagram & Physics beyond the Standard Model.
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TL;DR: This new version of OpenLoops, an automated generator of tree and one-loop scattering amplitudes based on the open-loop recursion, is presented, equipped with an automated system that avoids Gram-determinant instabilities through analytic methods in combination with a new hybrid-precision approach.
Abstract: We present the new version of OpenLoops, an automated generator of tree and one-loop scattering amplitudes based on the open-loop recursion. One main novelty of OpenLoops 2 is the extension of the original algorithm from NLO QCD to the full Standard Model, including electroweak (EW) corrections from gauge, Higgs and Yukawa interactions. In this context, among several new features, we discuss the systematic bookkeeping of QCD-EW interferences, a flexible implementation of the complex-mass scheme for processes with on-shell and off-shell unstable particles, a special treatment of on-shell and off-shell external photons, and efficient scale variations. The other main novelty is the implementation of the recently proposed on-the-fly reduction algorithm, which supersedes the usage of external reduction libraries for the calculation of tree-loop interferences. This new algorithm is equipped with an automated system that avoids Gram-determinant instabilities through analytic methods in combination with a new hybrid-precision approach based on a highly targeted usage of quadruple precision with minimal CPU overhead. The resulting significant speed and stability improvements are especially relevant for challenging NLO multi-leg calculations and for NNLO applications.
239 citations
Cites background or methods from "Recola2: REcursive Computation of O..."
...(iii) complex_mass_scheme=2 corresponds to the implementation of the complex-mass scheme in Recola [20]....
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...Nowadays, thanks to a variety of modern techniques [1–9], one-loop calculations can be carried out with a number of automated and widely applicable programs [10–20] that have strongly boosted the field of precision phenomenology....
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TL;DR: Sherpa as discussed by the authors is a general-purpose Monte Carlo event generator for the simulation of particle collisions in high-energy collider experiments, which is heavily used for event generation in the analysis and interpretation of LHC Run 1 and Run 2 data.
Abstract: Sherpa is a general-purpose Monte Carlo event generator for the simulation of particle collisions in high-energy collider experiments. We summarize essential features and improvements of the Sherpa 2.2 release series, which is heavily used for event generation in the analysis and interpretation of LHC Run 1 and Run 2 data. We highlight a decade of developments towards ever higher precision in the simulation of particle-collision events.
203 citations
TL;DR: In this paper, the authors present the key features relevant to the automated computation of all the leading and next-to-leading order contributions to short-distance cross sections in a mixed-coupling expansion, with special emphasis on the first sub-leading NLO term in the QCD+EW scenario, commonly referred to as NLO EW corrections.
Abstract: We present the key features relevant to the automated computation of all the leading- and next-to-leading order contributions to short-distance cross sections in a mixed-coupling expansion, with special emphasis on the first subleading NLO term in the QCD+EW scenario, commonly referred to as NLO EW corrections. We discuss, in particular, the FKS subtraction in the context of a mixed-coupling expansion; the extension of the FKS subtraction to processes that include final-state tagged particles, defined by means of fragmentation functions; and some properties of the complex mass scheme. We combine the present paper with the release of a new version of MadGraph5_aMC@NLO, capable of dealing with mixed-coupling expansions. We use the code to obtain illustrative inclusive and differential results for the 13-TeV LHC.
203 citations
TL;DR: In this article, the authors describe an algorithm for the reconstruction of multivariate polynomials and rational functions from their evaluation over finite fields using machine-size integers in statically-typed languages.
Abstract: Several problems in computer algebra can be efficiently solved by reducing them to calculations over finite fields. In this paper, we describe an algorithm for the reconstruction of multivariate polynomials and rational functions from their evaluation over finite fields. Calculations over finite fields can in turn be efficiently performed using machine-size integers in statically-typed languages. We then discuss the application of the algorithm to several techniques related to the computation of scattering amplitudes, such as the four- and six-dimensional spinor-helicity formalism, tree-level recursion relations, and multi-loop integrand reduction via generalized unitarity. The method has good efficiency and scales well with the number of variables and the complexity of the problem. As an example combining these techniques, we present the calculation of full analytic expressions for the two-loop five-point on-shell integrands of the maximal cuts of the planar penta-box and the non-planar double-pentagon topologies in Yang-Mills theory, for a complete set of independent helicity configurations.
194 citations
TL;DR: In this paper, a review of the field of electroweak corrections is presented, focusing on renormalization, one-loop techniques, modern amplitude methods and tools, separation of infrared singularities in real-emission corrections, electroweak issues connected with hadronic initial or final states in collisions, and the issue of unstable particles in quantum field theory together with corresponding practical solutions.
156 citations
References
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TL;DR: MadGraph5 aMC@NLO as discussed by the authors is a computer program capable of handling all these computations, including parton-level fixed order, shower-matched, merged, in a unified framework whose defining features are flexibility, high level of parallelisation and human intervention limited to input physics quantities.
Abstract: We discuss the theoretical bases that underpin the automation of the computations of tree-level and next-to-leading order cross sections, of their matching to parton shower simulations, and of the merging of matched samples that differ by light-parton multiplicities. We present a computer program, MadGraph5 aMC@NLO, capable of handling all these computations — parton-level fixed order, shower-matched, merged — in a unified framework whose defining features are flexibility, high level of parallelisation, and human intervention limited to input physics quantities. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the LHC and to a 1-TeV e + e − collider. While next-to-leading order results are restricted to QCD corrections to SM processes in the first public version, we show that from the user viewpoint no changes have to be expected in the case of corrections due to any given renormalisable Lagrangian, and that the implementation of these are well under way.
6,509 citations
TL;DR: The review as discussed by the authors summarizes much of particle physics and cosmology using data from previous editions, plus 3,283 new measurements from 899 Japers, including the recently discovered Higgs boson, leptons, quarks, mesons and baryons.
Abstract: The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,283 new measurements from 899 Japers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as heavy neutrinos, supersymmetric and technicolor particles, axions, dark photons, etc. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as Supersymmetry, Extra Dimensions, Particle Detectors, Probability, and Statistics. Among the 112 reviews are many that are new or heavily revised including those on: Dark Energy, Higgs Boson Physics, Electroweak Model, Neutrino Cross Section Measurements, Monte Carlo Neutrino Generators, Top Quark, Dark Matter, Dynamical Electroweak Symmetry Breaking, Accelerator Physics of Colliders, High-Energy Collider Parameters, Big Bang Nucleosynthesis, Astrophysical Constants and Cosmological Parameters.
5,459 citations
TL;DR: In this article, a critical review of the current status of cosmological nucleosynthesis is given, where the baryon-to-photon ratio of deuterium and helium-4 is consistent with the independent determination of $\eta$ from observations of anisotropies in the cosmic microwave background.
Abstract: A critical review is given of the current status of cosmological nucleosynthesis. In the framework of the Standard Model with 3 types of relativistic neutrinos, the baryon-to-photon ratio, $\eta$, corresponding to the inferred primordial abundances of deuterium and helium-4 is consistent with the independent determination of $\eta$ from observations of anisotropies in the cosmic microwave background. However the primordial abundance of lithium-7 inferred from observations is significantly below its expected value. Taking systematic uncertainties in the abundance estimates into account, there is overall concordance in the range $\eta = (5.7-6.7)\times 10^{-10}$ at 95% CL (corresponding to a cosmological baryon density $\Omega_B h^2 = 0.021 - 0.025$). The D and He-4 abundances, when combined with the CMB determination of $\eta$, provide the bound $N_
u=3.28 \pm 0.28$ on the effective number of neutrino species. Other constraints on new physics are discussed briefly.
5,144 citations
TL;DR: The Mathematica package FeynArts as discussed by the authors is used for the generation and visualization of Feynman diagrams and amplitudes, with three levels, user-defined model files, and support for supersymmetric models.
1,796 citations
TL;DR: In this article, two program packages for evaluating one-loop amplitudes are presented, which can work either in dimensional regularization or in constrained differential renormalization, and they are shown to be equivalent to regularization by dimensional reduction.
1,564 citations