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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:

enter image description here

(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.

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  • $\begingroup$ I haven't heard that before, either. Was it a foreign language speaker? It's not clear to me what should be special about dark matter interaction that isn't seen in ordinary matter. The above is a sensitivity plot, right? $\endgroup$ – CuriousOne May 13 '16 at 20:48
  • $\begingroup$ @CuriousOne the English seemed solid to me, and it sounded like it was a standard jargon word in that subfield. I don't think the 'funnel' feature was peculiar to DM, it was something like a higher order correction to the sensitivity limit, it sounded like similar corrections would apply to any scattering interaction. And yes, it is a sensitivity plot. $\endgroup$ – Kyle Oman May 15 '16 at 6:17
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"Funnel" is used when talking about resonant annihilation of pairs of dark matter particles through an s-channel diagram. Depending on the type of mediator one speaks of Z funnel or Higgs funnel or, in models with two Higgs dublets like Supersymmetry, e.g. A funnel, thereby refering to a certain region in model space.

For dark matter particles with the right mass (in the funnel region), this resonant process will make the annihilation of the dark matter more efficient, making scenarios viable which would otherwise have too large (i.e. experimentally ruled out) relic amounts of thermally produced dark matter.

This does not help or hinder detection of dark matter but it has to be taken into account when making conclusions about which physical models are ruled out. You can find examples e.g. in Fig. 2 of https://arxiv.org/pdf/1308.3735v3.pdf and Fig. 14 of https://arxiv.org/pdf/1508.06608v2.pdf. Note that these plots are not from direct dark matter searches like the one you show above.

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