Feynman Diagram question

kokolovehuh

Hi all,
I'm just getting started on particle physics and I have a few foolish questions about drawing feynman diagram.
First, when do we draw the gauge bosons(such as W) vertically rather than horizontally through time?
Second, can we always replace mediator photon by Z boson? Does that represent real processes, real or virtual whatsoever?

Thank you so much

Regards

Owen

Nabeshin

This is completely dependent on the process! In general it just depends on which diagrams you can draw corresponding to the relevant physical situation. To take a concrete example, the first order contributions to Bhabha scattering contains both.

In general yes, and try to think about why we can make that specific substitution as opposed to any other and also why this diagram is typically neglected.

kokolovehuh

Thanks alot! It really helps

Parlyne

Note, though, that the reverse is not true. There is at least one type of situation in which a Z cannot be replaced by photon - interactions involving neutrinos.