# Do neutrinos have magnetic moment?

Do neutrinos have magnetic moment? If yes, should not it indicate existence of preons?

• Particle physics model predictions rely on calculating sums of Feynman diagrams,which in higher orders will include electromagnetic vertices , even though the direct vertices with neutrinos are weak. There is no need for preons. – anna v Jan 24 '18 at 4:57

Neutrinos "do" have a magnetic moment, in the sense that the Standard Model (with minimal additions to permit the neutrino to have mass) predicts that neutrinos acquire a very, very small magnetic moment. Something like $10^{-19}$ times the magnetic moment of the electron.

On the other hand, the magnetic moment of neutrinos has never been measured (only upper bounds have been set), so we don't know if neutrinos really do have a magnetic moment.

Considering that models that don't contain preons predict a magnetic moment, no, this would imply nothing about preons.

A nice link thanks to @annav: Status and perspectives of neutrino magnetic moments

• – anna v Jan 24 '18 at 4:52
• How a neutral particle can have a magnetic moment if it does not have an internal structure? – Anixx Jan 24 '18 at 5:19
• It acquires one from loop diagrams. You can think of it like this: there's a chance for a neutrino to turn into a virtual W boson/charged lepton loop and then back. And since that interaction only couples to one helicity of the neutrino and those two particles are charged, you get a magnetic moment this way. – Chris Jan 24 '18 at 5:29
• This seems not to contradict preons: the W boson and the lepton can consist of preons. – Anixx Jan 24 '18 at 8:37
• It doesn't contradict preons, but it also doesn't suggest them or require them. – Mitchell Porter Jan 24 '18 at 9:24