Annihilation into non-SM particles

Asked by Nishita


We have a model with an extra new particle in the dark sector which can decay as P > SM SM. The annihilation mechanism should be DM DM > P P (followed by P > SM SM but that can be assumed to always happen nearly instantaneously). However, we find that unless the final states are known SM particles, the annihilation mode is not taken into account at all.

Could you advise how we can add this annihilation mode to the list?


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Daniele Massaro (dmassaro) said :

Hello Nishita,

in what framework (relic density, indirect detection) did you find that behaviour? From our side we checked that in the presence of other dark sector particles (that are Z2-even, with the dark matter Z2-odd), the code generates all the annihilation processes. I assume your particle P is Z2-even, given it can decay into SM, so I would expect the code to include the process you mentioned. Can you be more specific on the commands you are running?

Thank you.

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Nishita (nish-des) said :

Thanks for your reply. The model contains two scalars -- let's call them P and D and the dark matter field D does not have any direct interactions with the SM. The only interaction it has is of the form P^2 D^2 which would deplete D via DD -> PP when P is kinematically accessible.

If we add a scalar^3 term of the form DDS with S f fbar coupling, it does show DD->ffbar, but not when it's only DD -> PP. The mass of P is set to be smaller than mass of D.

The only command we run is "generate relic_density" after setting "define dark matter D".

(The actual name of the particle in the UFO is not D, but Pc but I'm using D here for consistent notation and to avoid confusion. Mentioning this in case you were concerned about it having the same name as down-type quarks).

Is there some specific way to set Z2 even/odd other than having the Lagrangian via UFO?

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Daniele Massaro (dmassaro) said :

Hi Nishita,

the Z2 symmetry of the different particles is computed automatically once one defines the dark matter candidate with the command "define darkmatter". The program loops over the vertices of the model, obtaining the Z2 parity of all of the new particles, according to the rule dark matter-odd and SM particles-even.
Could you send use the UFO model so that we can check what could be the issue? I can turn this question in a bug report, so that you can attach files.

Thank you.
Daniele Massaro

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