Advanced/retarded Feynman propagator?

[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.

 

[Greg Bernhardt]

Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?