Feynman Diagram Vertices: What needs to be conserved?

[McLaren Rulez]

Hi,

I'm taking introductory particle physics and this is related to the first couple of chapters in Griffiths. If I draw a Feynman diagram for a particular process, what conservation laws must hold at each vertex? Mainly looking at QED processs but as far as I can work out energy and momentum are the main ones. It also seems that one cannot go from one lepton family to another or one quark family to another at a vertex. Anything else I'm missing or incorrectly stating?

Also, when we have virtual particles, are there any restrictions (apart from those above) on what I can use as a virtual particle?

Somehow, its not too clear in Griffiths and I can't find a set of rules online either. Thank you!

 

[LightHero]

In addition to energy and momentum, the conservation laws that must hold at each vertex in a Feynman diagram are those related to charge (e.g. electric charge), angular momentum, spin, and baryon number (the number of baryons minus the number of anti-baryons). In QED processes, you cannot go from one lepton family to another or one quark family to another at a vertex. When dealing with virtual particles, you must also take into account the conservation of energy and momentum, as well as any other conserved quantities relevant to the process being considered (e.g. electric charge, angular momentum, spin, etc.). However, there is no restriction on what type of particle can be used as a virtual particle, as long as the conservation laws are satisfied.