2
$\begingroup$

Feynman rules for derivative couplings always make me confused. For example, the derivative in $gV^\mu\phi^+\partial_\mu\phi^-$ will give you $\pm ip_{-\mu}$, where $\pm$ depends on whether the particle is outgoing or incoming.

I found "$-ip_{-\mu}$ for incoming" in Peskin & Schroeder's QFT book, BUT I also found "$-ip_{-\mu}$ for outgoing" in some other literature. So I'm wondering if the latter one is wrong. Or are they just in different conventions so that we can choose either of them?

$\endgroup$
1
$\begingroup$

The sign convention used here depends on the metric signature convention and on the convention used in defining the coupling. In Penskin and Schroeder, for example, the QED coupling $e$ is defined to be negative, so an extra minus sign may be found if comparison are made to other texts.

I recommend reading through Matthew Schwartz's Appendix A: Sign Conventions: http://isites.harvard.edu/fs/docs/icb.topic1146657.files/A-Conventions.pdf .
In section 3, he does an excellent job of addressing this question and discusses the discrepancies with other texts.

$\endgroup$
0
$\begingroup$

Yes, It's just a convention. During your calculations you can put the minus sign for outgoing particles and plus for incoming or put the minus sign for incoming, but you can't use both of them at the same time.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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