The spin magnetic moment of a charged, spin-1/2 particle is(adsbygoogle = window.adsbygoogle || []).push({});

$$g \frac e {2m} \frac \hbar 2$$

where g is the g-factor (2 for any particle in tree-level approximation, 2.00231930436182 for electron),

e is charge

m is mass

##\frac \hbar 2## is spin

But with zero mass this expression does not make sense.

What does it mean?

"Massless charged fermions are not allowed in quantum theories"?

Or "massless charged fermions have infinite magnetic moment"??

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# I Magnetic moment of a massless charged Fermion?

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