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I have a question about majorana neutrinos.
Majorana particles are particles that are their own antiparticle. From this I would argue that they need to have all quantum numbers equal to zero. My question is: what about the weak isospin? This cannot be zero, as neutrinos partecipate into weak interactions.
Thank you for any help on this.
You say about Majorana fermions:
"From this I would argue that they need to have all quantum numbers equal to zero."
which is not true. Charge conjugation is defined on Dirac spinors as $\psi^c := \mathrm{i}\gamma^0\gamma^2\bar\psi^T$. Being Majorana means $\psi^c = \psi$. While this would imply the spinor has zero electric charge (and zero all other $\mathrm{U}(1)$ charges, if there were any, probably), this does not imply anything about the representations of the other gauge groups it transforms in.
