Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am currently struggling with the formula for an exact current in QFT, a fermion with an upcoming momentum $p$ and an outgoing momentum $p'$. My problem is to show whether or not a term of the form $\bar{u}(p')F(q^2)i\sigma^{\mu\nu}(p+p')^{\nu}$ where $\sigma^{\mu\nu}=\frac{i}{2}[\gamma^{\mu},\gamma^{\nu}]$. I would like it to be forbidden by current conservation but I can't prove it, is my intuition wrong?

share|cite|improve this question
up vote 1 down vote accepted

Your term is allowed, and in fact present in QED. It gives the anomalous magnetic form factor contribution to the current. In QED, The number $2F(0)$ is the anomalous magnetic moment of the electron. See Peskin/Schroeder p.186-188.

share|cite|improve this answer
Thanks, managed to show that this term is proportional to $\bar{u}(p')\gamma^{\mu}u(p)$ by using the Dirac equation. – toot Mar 15 '12 at 17:56

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.