# What are the quantum numbers of Majorana neutrinos?

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.

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.
• Under the standard seesaw mechanism, doesn't "Majorana neutrinos" mean not Majorana bispinors satisfying $\Psi^c = \Psi$, but instead Dirac spinors (which transform nontrivially under charge conjugation) with Majorana mass terms? Apr 11, 2020 at 20:49