| 1. |
- Alnefjord, Joakim, et al.
(författare)
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A Brief Look at the Chirality-Flow Formalism for Standard Model Amplitudes
- 2021
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Ingår i: The Ninth Annual Conference on Large Hadron Collider Physics : LHCP2021 - LHCP2021. - 1824-8039. ; 397
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Konferensbidrag (refereegranskat)abstract
- Inspired by the flow description of su(N) colour calculations, we recently showed how to simplify the spinor-helicity formalism (at the algebra level two copies of complexified su(2)) by treating each Weyl spinor as part of a flow line with definite chirality and momentum. This formalism, dubbed the chirality-flow formalism, eliminates all non-trivial algebra from tree-level spinor-helicity calculations, thus allowing the shortest possible route from Feynman diagrams to complex numbers (spinor inner products). In this presentation, we briefly introduce the main features of this method and show some examples.
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| 2. |
- Alnefjord, Joakim, et al.
(författare)
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The Chirality-Flow Formalism for Standard Model Calculations
- 2022
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Ingår i: International Workshop on Lie Theory and Its Applications in Physics. - Singapore : Springer Nature Singapore. - 2194-1017 .- 2194-1009. - 9789811947506 ; 396, s. 387-394
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Konferensbidrag (refereegranskat)abstract
- Scattering amplitudes are often split up into their color (su(N) ) and kinematic components. Since the su(N) gauge part can be described using flows of color, one may anticipate that the su(2 ) ⊕ su(2 ) kinematic part can be described in terms of flows of chirality. In two recent papers we showed that this is indeed the case, introducing the chirality-flow formalism for standard model calculations. Using the chirality-flow method—which builds on and further simplifies the spinor-helicity formalism—Feynman diagrams can be directly written down in terms of Lorentz-invariant spinor inner products, allowing the simplest and most direct path from a Feynman diagram to a complex number. In this presentation, we introduce this method and show some examples.
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| 3. |
- Alnefjord, Joakim, et al.
(författare)
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The chirality-flow formalism for the standard model
- 2021
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:4
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Tidskriftsartikel (refereegranskat)abstract
- In a recent paper we introduced the chirality-flow formalism, a method for simple and transparent calculations of Feynman diagrams based on the left- and right-chiral sl(2 , C) nature of spacetime. While our previous work focused on massless QED and QCD at tree-level, we here extend the chirality-flow formalism to the full (tree-level) Standard Model, including massive particles and electroweak interactions – for which the W-interaction simplifies elegantly due to its chiral nature. We illustrate how values of Feynman diagrams can be immediately written down with some representative examples.
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| 4. |
- Andersen, Jeppe R., et al.
(författare)
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Les Houches 2017: Physics at TeV Colliders Standard Model Working Group Report
- 2018. - 07977
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This Report summarizes the proceedings of the 2017 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, (II) theoretical uncertainties and dataset dependence of parton distribution functions, (III) new developments in jet substructure techniques, (IV) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (V) phenomenological studies essential for comparing LHC data from Run II with theoretical predictions and projections for future measurements, and (VI) new developments in Monte Carlo event generators.
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| 5. |
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| 6. |
- Bellm, Johannes, et al.
(författare)
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Herwig 7.2 release note
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:5
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Tidskriftsartikel (refereegranskat)abstract
- A new release of the Monte Carlo event generator Herwig (version 7.2) is now available. This version introduces a number of improvements over the major version 7.0, notably: multi-jet merging with the dipole shower at LO and NLO QCD; spin correlations in both the dipole and angular-ordered parton showers; an improved choice of evolution variable in the angular-ordered parton shower; improvements to mass effects and top decays in the dipole shower, improvements to the simulation of multiple-parton interactions, including diffractive processes; a new model for baryonic colour reconnection; improvements to strangeness production; as well as a new tune of the hadronisation parameters and support for generic Lorentz structures in BSM models. This article illustrates new features of versions 7.1 and 7.2.
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| 7. |
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| 8. |
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| 9. |
- Cormier, Kyle, et al.
(författare)
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Parton showers and matching uncertainties in top quark pair production with Herwig 7
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:11
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Tidskriftsartikel (refereegranskat)abstract
- We evaluate the theoretical uncertainties in next-to-leading order plus parton shower predictions for top quark pair production and decay in hadronic collisions. Our work is carried out using the Herwig 7 event generator and presents an in-depth study of variations in matching schemes with two systematically different shower algorithms, the traditional angular-ordered and alternative dipole shower. We also present all of the required extensions of the Herwig dipole shower algorithm to properly take into account quark mass effects, as well as its ability to perform top quark decays. The predictions are compared at parton level as well as to Large Hadron Collider data, including in the boosted regime. We find that the regions where predictions with a non-top-quark-specific tune differ drastically from data are plagued by large uncertainties which are consistent between our two shower and matching algorithms.
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| 10. |
- Figueroa, Diogenes, et al.
(författare)
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Updates to the one-loop provider NLOX
- 2022
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 270
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Tidskriftsartikel (refereegranskat)abstract
- In this release note we describe the 1.2 update to NLOX, a computer program for calculations in high-energy particle physics. New features since the 1.0 release and other changes are described, along with usage documentation. New version program summary: Program title: NLOX Developer's repository link: http://www.hep.fsu.edu/~nlox Licensing provisions: CC BY NC 3.0 Programming language: C++. Fortran interface available, and Fortran compiler required for dependencies. Journal reference of previous version: Comput. Phys. Commun. 257 (2020) 107284 Does the new version supersede the previous version?: Yes Reasons for the new version: We have added several new features to NLOX, and made significant stability and efficiency improvements. The new features provide new types of output, and more flexibility for user input. These features are largely motivated to simplify interfacing NLOX with other automated tools, Monte Carlo and real-radiation providers in particular. Occasionally in a Monte Carlo run using NLOX instabilities are discovered in the loop results of NLOX in certain corners of phase space. While the original version had methods to detect these instabilities, and partially correct for them, the latest version has additional methods of detecting instabilities, and existing methods are improved. This version has better reliability and specificity of detection, and a higher success rate of correction. Summary of revisions: We have added new output modes. The first new mode allows the user to isolate contributing pieces in the amplitude-squared in powers of the constants αe and αs. NLOX is also now capable of producing color-correlated output for Born-level matrix elements, required for interfacing to real-radiation providers. We have added support for the Les Houches standard interface function, OLP_SetParameter, implemented as NLOX_OLP_SetParameter. This allows users to set certain parameters, for our purposes coupling constants, masses, widths, the number of light and heavy quark flavors, and the renormalization scale. Previously these were runtime constants in NLOX, requiring editing an input file, or specialized functions to set after program initialization. We have improved the numerical stability of NLOX substantially in this release. First, the stability tests performed internally by the TRed library have been improved. In particular, we have devised a better metric for determining configurations of phase space where the Gram determinant is small, and therefore the default reduction numerically unstable, by comparing the determinant, a measure of the “volume” of the matrix, to a maximal volume spanned by the vectors of the matrix. Second, we have interfaced with higher-precision external libraries where available and necessary. The thresholds for recomputation in higher precision and warning flags for internal failure have been adjusted accordingly, allowing for fewer recomputations, a higher sensitivity to phase space points giving numerically incorrect results, and more specificity to flagging points as failed to the user. Finally, we have implemented new routines that compute the IR pole structure of the real emission corresponding to the virtual routines of NLOX, as a final check of the amplitude squared. These routines are used automatically to determine an estimated accuracy of the result returned through the standard Les Houches flag acc of the user function NLOX_OLP_EvalSubProcess. We have retooled the generation of processes provided in downloadable packages to reduce expression sizes and eliminate some common structures, resulting in significantly smaller code sizes, sometimes a factor of two smaller than in the 1.0 version. For a more complete discussion of the changes in this release, please see the accompanying document in the package, nlox-1.2.0.pdf. Nature of problem: The computation of higher-order terms in the coupling expansion of Standard Model scattering amplitudes is required for precision studies in collider experiments. Techniques for computing the first corrections are well-known, and are now suited to automation. We wish to provide code that calculates virtual (one-loop) quantum chromodynamics and electroweak corrections for desired amplitudes using a package that automates the production of this code. Solution method: We use Python scripts and a computer algebra system, FORM, to reduce virtual amplitudes to C++ code and data based on Feynman rules of the Standard Model. The scripts perform a tensor decomposition of the one loop integrals to reduce each amplitude to a dependence on tensor integral coefficients. These coefficients are called at runtime by the provided library TRed, which performs tensor reduction into base (scalar) coefficients at runtime. The scripts identify repeated structures to be calculated once in the produced code for efficiency. The tensor reduction code is designed such that needed tensor coefficients need to be computed only once per evaluation of the desired amplitude, and are built recursively from other needed coefficients. Additional comments including restrictions and unusual features: The code-producing scripts are not provided in this release, only fixed libraries such as TRed and required interface code for pre-generated processes. Some processes are provided with this release, with others available upon request. • Required External Dependencies: QCDLOOP 1.95, ONELOOP 3.6 (available for download in utility tarball). • Required Compilers: gcc 4.6 or higher. Interface to certain optional libraries requires C++ 11 support found in gcc 4.7 or higher. • Operating System: Linux, MacOS.
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| 11. |
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| 12. |
- Honeywell, Steve, et al.
(författare)
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NLOX, a one-loop provider for Standard Model processes
- 2020
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 257
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Tidskriftsartikel (refereegranskat)abstract
- NLOX is a computer program for calculations in high-energy particle physics. It provides fully renormalized scattering matrix elements in the Standard Model of particle physics, up to one-loop accuracy for all possible coupling-power combinations in the strong and electroweak couplings, and for processes with up to six external particles.
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| 13. |
- Lifson, Andrew, et al.
(författare)
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Introducing the chirality-flow formalism
- 2020
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Ingår i: Acta Physica Polonica B. - 0587-4254. ; 51:6, s. 1547-1557
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Tidskriftsartikel (refereegranskat)abstract
- In QCD, we are used to describing the SU(3) color space in terms of a flow of color. At the algebra level, the Lorentz group consists of two copies of the (complexified) su(2) algebra, so one may anticipate that a similar way of thinking about the spacetime structure of scattering amplitudes should exist. In this article, we argue that this is indeed the case, and introduce the chirality-flow formalism for massless tree-level QED and QCD. Within the chirality-flow formalism, scattering amplitudes can directly be written down in terms of Lorentz-invariant spinor inner products, similar to how the color structure can be described in terms of a color flow.
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| 14. |
- Lifson, Andrew, et al.
(författare)
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The chirality-flow formalism
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:11
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Tidskriftsartikel (refereegranskat)abstract
- We take a fresh look at Feynman diagrams in the spinor-helicity formalism. Focusing on tree-level massless QED and QCD, we develop a new and conceptually simple graphical method for their calculation. In this pictorial method, which we dub the chirality-flow formalism, Feynman diagrams are directly represented in terms of chirality-flow lines corresponding to spinor inner products, without the need to resort to intermediate algebraic manipulations.
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