1. Oct 30, 2014

### thoughtgaze

is there a discussion somewhere on the notion of an advanced or retarded feynman propagator.

i don't mean the advanced or retarded propagator juxtaposed against the feynman propagator. I mean the feynman propagator itself with a theta step function multiplied by it to effectively give an advanced/retarded feynman propagator.

2. Nov 4, 2014