FeynRules - Feynman rules made easy (0806.4194v1)

Abstract: In this paper we present FeynRules, a new Mathematica package that facilitates the implementation of new particle physics models. After the user implements the basic model information (e.g. particle content, parameters and Lagrangian), FeynRules derives the Feynman rules and stores them in a generic form suitable for translation to any Feynman diagram calculation program. The model can then be translated to the format specific to a particular Feynman diagram calculator via FeynRules translation interfaces. Such interfaces have been written for CalcHEP/CompHEP, FeynArts/FormCalc, MadGraph/MadEvent and Sherpa, making it possible to write a new model once and have it work in all of these programs. In this paper, we describe how to implement a new model, generate the Feynman rules, use a generic translation interface, and write a new translation interface. We also discuss the details of the FeynRules code.

• The paper presents FeynRules as an automated tool to derive Feynman rules from Lagrangians, significantly reducing manual errors in model implementation.
• It details a versatile methodology with translation interfaces for platforms like CalcHEP, FeynArts, MadGraph, and Sherpa to facilitate accurate computations.
• Validation against established models confirms FeynRules’ robust performance, accelerating research and development in beyond the Standard Model physics.

Overview of FeynRules: Automating the Derivation of Feynman Rules

The paper, "FeynRules - Feynman rules made easy," introduces a novel computational tool designed to streamline the process of deriving Feynman rules from a Lagrangian in new particle physics models. FeynRules, a Mathematica package developed by Neil D. Christensen and Claude Duhr, addresses the technical challenges associated with model implementation across various Feynman diagram calculation programs. This paper systematically delineates the functionalities of FeynRules and its interfaces with major calculation platforms such as CalcHEP/CompHEP, FeynArts/FormCalc, MadGraph/MadEvent, and Sherpa.

The innovation of FeynRules lies in its ability to automate the derivation of interaction vertices from the Lagrangian using canonical quantization methods. This is particularly valuable for physicists exploring beyond the Standard Model (BSM) theories where unique spectra of fields and interactions are anticipated at the TeV scale. As LHC experiments continue to explore this energy regime, efficient computational tools like FeynRules become indispensable.

Key Features and Functionality

FeynRules reduces the complexity and potential errors in initializing new models by allowing users to define model files in a generic format. This generic format can then be translated into the specific required syntax for different computational tools, thus eliminating the need for redundant, manual model input for each program—a process that has traditionally been tedious and error-prone.

FeynRules is equipped with various features:

1. Model File Structure: The core component where users define particles, their properties, and interactions fundamentally expressed in a Lagrangian. The paper elaborates on how users can specify models, ensuring compliance with quantum field theory constraints such as Lorentz and gauge invariance.
2. Vertex Generation: After defining the model, FeynRules derives vertices automatically. This functionality is essential for complex calculations, facilitating comparisons between theoretical predictions and experimental data from high-energy physics colliders.
3. Translation Interfaces: These modules within FeynRules convert the generalized model and vertex data into formats compatible with various Feynman diagram calculators, leveraging each tool's unique strengths for different aspects of BSM physics exploration.
4. ToolBox: The package includes a suite of diagnostic and utility functions to test and verify the properties of the model and ensure that the derived terms are correct, such as checking the Hermiticity of the Lagrangian or ensuring correct kinetic term normalization.

Numerical Results and Software Validation

The efficacy of FeynRules is validated through its application to widely-studied physics models, including the Standard Model and others like the Three-Site Model. By comparing its output with established results and existing implementations, FeynRules demonstrates reliable coherence with theoretical expectations. Numerical validations against cross-sections and other model properties computed in established packages are detailed, underscoring its robustness.

Implications

The introduction of FeynRules significantly streamlines the prototyping process of new physics models in theoretical high energy physics. By providing a consistent, automated approach to deriving complex Feynman rules and facilitating their application across different computational platforms, FeynRules accelerates the pace of research and experimentation.

Future Prospects

The discussion points to potential expansions for FeynRules. These include developing additional interfaces for other computational packages not yet supported, thereby broadening the toolkit available to particle physicists. As computational demands evolve with new physics theories and experimental results, FeynRules is positioned to continually adapt and serve its role in advancing theoretical physics exploration.

The contributions of FeynRules are a testament to the critical intersection of computational methods and theoretical physics, offering a pathway to handle the increasingly complex landscape of particle interactions beyond the Standard Model.