How to Install FeynRules: A Step-by-Step Guide for High-Energy Physicists

 

Introduction: Why FeynRules Matters

If you're working in particle physics, quantum field theory, or Beyond-the-Standard-Model (BSM) research, you’ve probably heard of FeynRules. This powerful Mathematica package lets you generate Feynman rules for new particle interactions and export them to Monte Carlo tools like MadGraph, CalcHEP, or Sherpa.

But installing it can be tricky—especially if you're new to computational physics tools.

In this guide, I’ll walk you through installing FeynRules smoothly, avoiding common pitfalls, and verifying your setup. I’ve used FeynRules for BSM model-building in my research, and I’ll share pro tips from CERN physicists along the way.

What You’ll Need Before Installing FeynRules

Before diving in, make sure you have:

✅ Mathematica (v10.0 or later) – FeynRules runs as a Mathematica package.
✅ A working Python environment (For some exports, like UFO models).
✅ Basic terminal/command-line familiarity (For path configurations).

Step 1: Downloading FeynRules

1. Go to the official FeynRules website:

2. 1. Download the latest stable version (e.g., FeynRules-X.X.X.zip).

   2. Extract the ZIP file to a preferred directory (e.g., ~/PhysicsTools/FeynRules).

   Common Mistake:
   Putting FeynRules in a path with spaces or special characters (like My Documents) can cause errors. Stick to simple paths like /Users/YourName/Physics/FeynRules.

Step 2: Setting Up Mathematica to Recognize FeynRules

Now, you need to tell Mathematica where to find FeynRules.

Method 1: Manual Path Setup (Recommended for Beginners)

1. Open Mathematica.

2. Run this command in a notebook:

   mathematica

   AppendTo[$Path, "~/PhysicsTools/FeynRules"];  

   (Replace the path with your actual FeynRules directory.)

Method 2: Permanent Path Configuration (For Frequent Users)

To avoid re-entering the path every time:

1. Find your Mathematica base directory (run $UserBaseDirectory in Mathematica).

2. Navigate to Autoload > FeynRules and place the package there.

Step 3: Testing Your FeynRules Installation

Let’s make sure everything works.

1. Load the package:

   mathematica

   << FeynRules`  

2. Run a simple test:

   mathematica

   LoadModel["SM.fr"];  

   (This loads the Standard Model pre-installed with FeynRules.)

✅ If you see no errors, your installation is successful!

❌ If you get an error, check:

• Did you extract the files correctly?

• Is the path spelled right?

• Does Mathematica have permission to access the folder?

Step 4: Exporting Models to MadGraph/UFO Format

One of FeynRules’ best features is exporting models for event generators. Here’s how:

1. Load your model (e.g., a custom BSM Lagrangian):

   mathematica

   LoadModel["MyNewModel.fr"];  

2. Export to UFO format (for MadGraph):

   mathematica

   WriteUFO[MyNewModel];  

3. Find the generated UFO folder (usually in the same directory).

Real-World Example:
A PhD student at ETH Zurich used this to simulate Dark Matter signals in MadGraph, leading to a published paper!

Final Thoughts: Next Steps After Installation

Now that FeynRules is installed, you can:

• Define custom Lagrangians for your research.

• Generate Feynman diagrams automatically.

• Simulate collisions in MadGraph.

Want to go deeper? Check out the official FeynRules manual or join the HEP software forums for advanced tips.