Source-linked AI summary
LanHEP - a package for automatic generation of Feynman rules from the Lagrangian. Updated version 3.2
A. Semenov
TL;DR
LanHEP generates Feynman rules from compact Lagrangians, with outputs for several model formats. Version 3.2 adds UFO output, color sextets, vertex-coefficient extraction, and aliases that define substitution rules and new statements.
Problem
Generating Feynman rules and model outputs from Lagrangians is the task LanHEP addresses.
Source: Introduction · p. 1Method
LanHEP reads compact Lagrangians and generates Feynman rules, while new features add UFO output, color-sextet support, vertex-expression extraction, and aliases for substitutions and statements.
Source: Introduction · p. 1, §1 · p. 1, §2 · p. 2Results
Version 3.2 provides UFO output, supports color sextets, and adds CoefVrt extraction and alias-defined substitution rules and statements.
Source: Introduction · p. 1, §1 · p. 1, §2 · p. 2Takeaways & Limitations
LanHEP generates outputs that can be used to start calculations in new physical models, and its aliases can define statements for model use.
Source: Introduction · p. 1, §3 · p. 3CoefVrt cannot handle higher-order vertices containing products of several momenta.
Source: §2 · p. 2
Abstract
from arXiv · showhide
We present a new version 3.2 of the LanHEP software package. New features include UFO output, color sextet particles and new substutution techniques which allow to define new routines.
Introduction
LanHEP generates Feynman rules from compact Lagrangians and provides outputs for several modeling and calculation tools. Version 3.2 adds UFO output.
Introduction
- LanHEP reads compact Lagrangians and generates Feynman rules in CompHEP or CalcHEP model files, FeynArts format, or LaTeX tables.CompHEP and CalcHEP model files use physical fields and independent parameters, allowing calculations of processes in a new physical model.Source: Introduction · p. 1
- LanHEP can also generate one-loop counterterms in FeynArts format.Source: Introduction · p. 1
- Version 3.2 adds Feynman-rule output in UFO format.The format is selected with the -ufo command-line option.Source: Introduction · p. 1
1 Color sextets
LanHEP adds support for color-sextet particles in the color SU(3) representation. This support includes sextet interaction structures and is limited to CalcHEP output.
1 Color sextets
- LanHEP now supports particles in the 6-dimensional representation of color SU(3), called color sextets.Source: §1 · p. 1
- The particle definitions use color c6 for sextets and color c6b for anti-sextets.The passage describes matrices for sextet interactions with triplets and gluons, and a covariant-derivative form using the gluon interaction matrix.Source: §1 · pp. 1–2
- Color sextets are supported only for CalcHEP output.Source: §1 · p. 2
2 Coefficients in the vertices
LanHEP’s CoefVrt function extracts selected expressions from generated vertices. Its options select tensor structures and expression components, with stated limits on momentum-dependent terms.
2 Coefficients in the vertices
- CoefVrt([particles],[options]) extracts a specified coupling expression from a generated vertex, supporting applications such as loop-induced Hγγ and Hgg contributions.The particle list identifies the vertex, while options specify its tensor structure and other extraction choices.Source: §2 · p. 2
- The supported tensor structures are 1, γ5, γµ, γµγ5, and pµ, and CoefVrt must be called separately for each structure.Source: §2 · p. 2
- The gamma and gamma5 options select specified γ-matrix terms; without them, extraction excludes terms containing γ-matrices.gamma selects γµ matrices, gamma5 selects γ5, and using both selects γµγ5.Source: §2 · p. 2
- moment(P) selects terms depending on particle P’s momentum, but higher-order vertices containing products of several momenta cannot be handled.Source: §2 · p. 2
- The re and im options return the real or imaginary part and can be combined with other options.Source: §2 · p. 2
- The abbr option uses abbreviations in returned expressions and is intended for long expressions.Source: §2 · p. 2
3 Aliases
Aliases define substitution rules applied to subsequent LanHEP statements, with argument-based patterns that can also expand into lists of statements. They support generated names and local temporary aliases for reusable model definitions.
3 Aliases
- Aliases define substitutions for subsequent statements, so a rename alias must precede the parameter declaration it changes.For example, alias mu=mue renames parameter µ throughout the model.Source: §3 · p. 2
- An alias can take arguments, and a symbol repeated on both sides of its definition matches any term in the actual expression.A leading space on a left-hand symbol makes it match any term; more general aliases must follow more specific ones, and unary plus prevents alias processing.Source: §3 · pp. 2–3
- Aliases can define lists of statements, allowing a single alias to stand for multiple model declarations.The syntax shown defines a list containing Stat1, Stat2, and further statements.Source: §3 · p. 3
- Statement-list aliases can generate new particle or parameter names from their arguments using the in operator or the # concatenation sign.The example uses # to form a scalar name and its mass parameter name.Source: §3 · p. 3
- A local statement creates temporary aliases for use within a block of statements.The example assigns M#name to sMass, then uses sMass in a scalar declaration.Source: §3 · p. 3