I came across some a new (to me) bit of terminology at a seminar recently. In the context of dark matter scattering off of atomic nuclei (but I think it may apply more generally for any particle scattering), what is a "funnel"? I can give a bit more to go on. It/they apparently appear as dips in the allowed parameter space in plots like this:
(The funnels are not seen here, I couldn't an example where they are illustrated, but would be happy to replace the image with one that actually illustrates what I'm talking about).
I asked the question at the seminar and got an answer involving something about resonance and "on-shell" production which I sort of followed, but I'm hoping for a better understanding.