When dealing with particle interactions, is there a straightforward way to work out the charge on the W boson?
In particular, the interactions I need to know the charge for are those involving a proton, neutron, an electron/positron and an electron neutrino/antineutrino. Is it easiest just to remember the charge (for AQA AS Physics exam)?
You have to look at the Feynman diagram to know if you can assign a charge.
Time-like $W$s carry the same charge as the initial and final states.
Space-like $W$s are ambiguous and you can not assign a unique charge to them, because you can't say which vertex came first in time.
For interaction that can occur through either time-like or space-like channels you still have the ambiguity.
