version: "1.0.0" name: ufo-generator description: Generate UFO (Universal FeynRules Output) model directories from FeynRules .fr files via Magnus cloud. Triggers when the user has a validated .fr model and needs a UFO model for MadGraph5.

UFO Generator

Overview

This skill generates UFO (Universal FeynRules Output) model directories from FeynRules .fr files using remote Mathematica execution via the Magnus cloud platform. UFO models are the standard interchange format between model-building tools (FeynRules) and Monte Carlo event generators (MadGraph5, Herwig, Sherpa).

Workflow

Step 1: Prepare the .fr File

Ensure the .fr file is validated (via feynrules-model-validator skill) and saved to disk. Know the Lagrangian symbol name (e.g., LSnew, LBSM).

Step 2: Generate the UFO Model

Execute the generate-ufo blueprint using magnus run (see magnus skill):

magnus run generate-ufo -- --model path/to/model.fr --lagrangian LSnew --output path/to/MyModel_UFO

Parameters:

The .fr file (and .rst if provided) is automatically uploaded via the FileSecret mechanism. On success, the UFO directory is automatically downloaded to --output.

WARNING: If --output points to an existing directory, it will be deleted and replaced by the download.

Model type is auto-detected:

• With M$GaugeGroups: loaded directly as standalone model
• Without M$GaugeGroups: BSM extension — SM.fr and SM restrictions (Massless.rst, DiagonalCKM.rst) are loaded automatically

Step 3: Read UFO Output Files

After successful generation, you must read the UFO files to understand the model before using it with MadGraph5:

1. `particles.py` — particle definitions with MG5 names and PDG codes

• Extract name field: the particle name to use in MG5 generate commands
• Extract pdg_code: needed for set param_card MASS <pdg> <value>

1. `parameters.py` — parameter definitions with SLHA block info

• Extract lhablock + lhacode: needed for set param_card <block> <code> <value>
• Extract value: default parameter values

This step is critical — particle names in MG5 come from the name field in particles.py, not from the ClassName in the .fr file.

Step 4: Verify UFO integrity

Check the result JSON (magnus job result <job-id>):

• success (bool): Whether generation succeeded
• ufo_path (str): Path to the downloaded UFO directory
• Any warnings about the generation process

If warnings are present, review the UFO files carefully before proceeding to MadGraph5.

Reference Documentation

• See references/ufo_format.md for detailed UFO directory structure, how to read particles.py and parameters.py, and mapping to MadGraph5 set param_card commands