maddump

massless DP electron-scatterings

Asked by Giacomo

I am trying to apply your code to the case of a massless dark photon. I have put
set my1 0.
set wy1 0.
and everything else is the same as the SHIP example (which I can get to run). If I do this, then the code runs fine until MadDump tries to calculate the e-DM scattering. It has been running for many hours and has not completed even the first scan. If I do this for a massive y1, it completes in a couple minutes.
I tried to use
decay pi0 > a xd xd~
but the same problem happens (even if I give a decay option for pion to (P.a, P.a) in decay.py file of the model.
Any suggestions to speed this up?

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English Edit question
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maddump Edit question
Assignee:
Luca Edit question
Solved by:
Giacomo
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Luca (lbuono) said : 		#1

Dear Giacomo,

that is a t-channel exchange. If you put to zero the mass of the dark photon and all the other masses involved are negligible,
then you are really hitting the forward singularity, corresponding to an almost on-shell dark photon (q^2->0, q the momentum transfer).
This is characteristic of Coloumb-like scattering processes like DM-e scattering.

So I would say, that you are a trying to compute an ill-defined physical quantity at the moment.

Cheers,
Luca

Revision history for this message
Luca (lbuono) said : 		#2

Dear Giacomo,

that is a t-channel exchange. If you put to zero the mass of the dark photon and all the other masses involved are negligible,
then you are really hitting the forward singularity, corresponding to an almost on-shell dark photon (q^2->0, q the momentum transfer).
This is characteristic of Coloumb-like scattering processes like DM-e scattering.

So I would say, that you are a trying to compute an ill-defined physical quantity at the moment.

Cheers,
Luca

Revision history for this message
Giacomo (gmarocco) said : 		#3

Yes, I needed to put a cut - thank you for pointing that out!