Drawing Feynman Diagrams for Fun and Profit with JaxoDraw

Joey Bernard — Fri, 22 Jun 2018 11:45:00 +0000

I've been covering chemistry software in my last few articles, so this time, I decided to move to physics and introduce a package called JaxoDraw. In physics, there's a powerful technique for visualizing particle interactions at the quantum level. This technique uses something called Feynman diagrams, invented by physicist Richard Feynman. These diagrams help visualize what happens when one or more particles have some kind of interaction. I say one or more because a single particle could spontaneously kick out other particle/anti-particle pairs and then swallow them back up again. Needless to say, quantum physics is weird.

When first developed, theoretical physics was mostly done either with pen and paper or on a chalkboard. Not much thought was given as to how you could render these drawings within a document being written on a computer. JaxoDraw is meant to help fill in that gap in document layout and provide the ability to render these drawings correctly and give output you can use in your own documents.

JaxoDraw is written in Java, so it should run under almost any operating system. Unfortunately, it isn't likely to be in the package repository for most distributions, so you'll need to download it from the project's website. But, because it's packaged as a jar file, it's relatively easy to run.

Download the binary package, unpack it on your machine, and then you'll want to open a terminal and change directory to the location where you unpacked JaxoDraw. You can start it simply by typing the following:


java -jar jaxodraw-2.1.0.jar

This opens a blank workspace where you can start your diagram. On the left-hand side of the window, you'll see a palette of all of the available drawing elements that you can use to generate your diagram.

Figure 1. When you first open JaxoDraw, you see a blank workspace where you can start diagramming your quantum particle interaction.

To see what's involved, let's draw an electron interacting with a photon. This happens when energy is absorbed or emitted by an electron. Since you're looking at an interaction, you'll want to start by selecting the vertex button from the palette and then draw one in the window. Coming into this vertex will be a fermion line for the electron and a photon line for the incoming electromagnetic energy. The interaction happens at the vertex, with a second fermion line coming out the other end. You can continue adding more elements, including loops or bezier lines, and you also have the choice of other particle types, such as scalar particles, ghost particles or gluons.

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Open-Source Physics on Linux

Joey Bernard — Mon, 22 Apr 2013 19:09:27 +0000

by Joey Bernard

My last several articles have covered lots of software for doing research in the sciences. But one important area I haven't covered in detail is the resources available for teaching the next generation of computational scientists. To fill this gap, you can use the code provided through the Open Source Physics project. This project is supported by the American Association of Physics Teachers (AAPT) and the National Science Foundation (NSF), and it offers several different packages for doing simulations and analysis.

The first thing Open Source Physics provides is an entire suite of Java applications that do simulations of different physical systems. Because these simulations are all written in Java, they can be run on operating systems other than Linux. The categories covered include astronomy, electricity and magnetism, classical mechanics, quantum mechanics, optics and relativity. On the main Web site, you either can do a specific search or browse by topic to find simulations. The simulation programs are packaged as .jar files, so you can download them and run them simply by typing:


java -jar filename.jar

This lets you run the simulation on your desktop. But, because these are Java programs, you can put them a Web site and run them within a browser. This means you can include them on your science site and show visitors simulations of the systems you might be trying to explain.

Figure 1. For example, starting up the simulation of sliding down an inclined plane also pops up some introductory material.

Some of the simulations provided by Open Source Physics have parameters that you can alter to change the runtime details of the simulation. These parameters might be items like masses, velocities or field strengths. If the simulation you are using does have settable parameters, there will be an option to save the model details off to a data file. You can do this by clicking File→Save Model. The data file is an XML file, so it should be relatively clear if you want to edit the file directly with a text editor. You then can reload these parameters in the simulation by clicking File→Load Module. This way, you can share models you've developed with other people by sharing the XML data file.

Figure 2. Saving a Run for Sharing with Other People

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