This is not possible because lepton number is not conserved. The lepton number of the LHS is 1, while the lepton number on the right is 2. I would say this is possible. My Feynman diagram is mediated by the [tex]z^0[/tex] boson, i'm pretty sure i've put the arrows in correctly. I would say this is possible. Once again, my Feynman diagram is mediated using the [tex]z^0[/tex] boson. This is not possible since baryon number is not conserved. I would appreciate it if someone could check these. I'm pretty sure they're right, i'm a little sceptical that the mediating boson in every possible case is the [tex]z^0[/tex]!