# Normal ordering in an interacting field theory

1. Dec 5, 2014

### SheikYerbouti

I am using Mandl and Shaw and Lahiri to get an introduction to QFT. Something I haven't seen discussed much or at all is whether the commutators or anti-commutators vanish for the normal ordering of a product of different field operators. As a concrete example, let's say that I want to normal order $\bar \psi^- \psi^+ \phi^-$, where $\psi$ is fermionic and $\phi$ is bosonic. Does the term pick up a minus sign or not and why?

2. Dec 10, 2014