## Feynman Diagrams for Beginners

And now for something completely different. I noticed on the arXiv a recent post with the following abstract:

We give a short introduction to Feynman diagrams, with many exercises. Text is targeted at students who had little or no prior exposure to quantum field theory. We present condensed description of single-particle Dirac equation, free quantum fields and construction of Feynman amplitude using Feynman diagrams. As an example, we give a detailed calculation of cross-section for annihilation of electron and positron into a muon pair. We also show how such calculations are done with the aid of computer.

The paper is indeed very nice and I recommend it to students everywhere. I had to teach myself what quantum field theory I know (which isn’t much) and I certainly wish I’d had an introduction like this to work through the examples!

In elementary courses on elementary particles Feynman diagrams are often presented as mere “cartoons” illustrating particular scattering or other processes, and they can play that role very usefully, but they are actually much more than that: they provide a neat and potentially very powerful way of doing real calculations.

Anyway, here’s an illustration:

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