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In other words, can mismatched particles and antiparticles react with each other? What about an up quark and anti-down quark?

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A left-handed up quark and a left-handed anti-down quark can annihilate into a W boson because of the nature of the weak interactions. Right-handed quarks do not interact via W boson because W boson is only left-handed, so they will not annihilate each other.

On the other hand, electron and an anti-muon can not annihilate each other in tree level because it would violate lepton number conservation. They can interact via a W boson but also an electron neutrino and a muon anti-neutrino would be created in the process.

There are some Grand Unification theories that allow lepton number violation and predict a rare process of annihilating electrons and muons into some new kind of bosons.

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    $\begingroup$ Why not exchange a neutrino in the t-channel? The electron could couple to W and an electrino, which would convert to a muino in flight, thanks to the PMNS mixing terms. It would be feeble effect, given the short life of a virtual neutrino, but ... $\endgroup$ – Bert Barrois May 4 '18 at 11:59
  • $\begingroup$ What are electrino and muino? $\endgroup$ – Oktay Doğangün May 4 '18 at 23:40
  • $\begingroup$ Neutrinos come in three distinct flavors or generations, which are the isospin partners of the electron, muon, and tauon, respectively -- just as in the quark zoo, U partners with D, C with S, and T with B. The PMNS matrix is the leptonic counterpart to the CKM matrix for quarks. $\endgroup$ – Bert Barrois May 5 '18 at 11:58
  • $\begingroup$ I know that. My question was about the terms, electrino and muino, that you have used in your comment. Are they different than electron neutrino and muon neutrino, respectively? Or just a short-hand naming? $\endgroup$ – Oktay Doğangün May 5 '18 at 14:48
  • $\begingroup$ Just short-hand. $\endgroup$ – Bert Barrois May 5 '18 at 15:57

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