- 12,960

- 536

So here goes:

Why does the term

[tex] \frac{e}{2} \bar{\Psi} (x) \Sigma^{\mu\nu} F_{\mu\nu}(x) \Psi (x)[/tex]

**NOT**appear in the classical lagrangian for the spin 1/2 parity invariant electrodynamics ?

p.s. I hope the notation is obvous, Sigma is the spin matrix = <i/2> times the commutator of the gamma matrices, the F is the e-m field tensor and the big Psi-s are the Dirac spinors.