Feynman diagram symbols

Feynman diagrams are intended to help us think about what happens but they cannot represent anything like a true image of interactions that take place in 3 dimensions.

We use this code on the diagrams, you might find different codes used by some publishers. This one code is used by the Institute of Physics and is common, but not universal.


Feynman diagrams

The particles entering and leaving the interaction (fermions) are shown as solid lines. Exchange particles shown here are either photons or a weak interaction bosons.

Changes in direction of the particles simply represents a change in momentum but they are not vector diagrams, there is no scale. An upward arrow on the line shows a real particle and a downward arrow is an antiparticle.

For example, interaction between two electrons.

The wavy line represents the energy change

or exchange particle which has a 

brief or virtual existence.

In this case a photon

Feynman diagram-Electrons interacting


More examples

Feynman diagram-beta decay

Feynman diagram-positrons interacting

Feynman diagram-positron emission


Feynman diagram-neutron neutrino interaction

Feynman diagram-electron capture



PDF and video lesson

You can download a PDF of these notes here:Feynman diagram notes

There is a short video lesson below which explains a little more thoroughly.