# The Dirac equation with anomalous magnetic moment term

1. Aug 4, 2011

### mtak0114

Hi could someone please explain the story (if there is one) about the Dirac equation with an anomalous magnetic moment term, I have seen this in several old papers but it never seems to be mentioned in text books. Was this an old confusion in formulating QFT. In this context I believe the Dirac equaiton with pauli term takes on the following form:

$-i\gamma^\mu(\partial_\mu-ieA_\mu)\psi + m\psi - (\frac 12 g-1)\frac{i e}{2m}F_{\mu\nu} S^{\mu\nu}\psi = 0$

where $S^{\mu\nu}$ are the generators of SL(2,C) and $F_{\mu\nu}$ is the electromagnetic tensor. I've never seen this extra term could you please tell me what it represents and if it is needed why