particle physics - Working out the charge of a W Boson

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)?

Answer

You have to look at the Feynman diagram to know if you can assign a charge.

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  Time-like $W$s carry the same charge as the initial and final states.

  
  



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  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.