For my Physics exam, I need to know 3 Feynman diagrams: beta-plus/minus decay, proton electron capturing, and neutrinos interacting with matter. I know that theres a W- in [tex]\beta[/tex]- decay, W+ in [tex]\beta[/tex]+ decay, which seems logical. However, in proton electron capture there is a W+ boson, and in a neutron-neutrino collision there is a W-. There seems to be no rule governing the charge of the boson. If there is, could someone please let me know!