MadGraph5_aMC@NLO

b b~ > h [QCD] by Yukawa coupling

Asked by Y. Z.

Hello!

Which model should I use if I want to
generate p(b) p(b~) > h > ... [QCD]
by Yukawa coupling?

With
loop_sm-no_mass
or so,
"Born diagrams could not be generated"

With loop_sm
or so,
"Fatal error in set_tau_min"

I have b b~ included in p

Is there a model that handles this process, or should I be hacking a model (if so, which model)?

Thanks!

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daniel camargo (dacamargov) said : 		#1

Hi Y.Z,

You can do that maybe using the HEFT model, you know it?. I guess you need only change t <--> b as well as the effective coupling.

Cheers

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Olivier Mattelaer (olivier-mattelaer) said : 		#2

Hi,

Note that this process has an inconsistency problem.
Indeed if you want to have the b in the beam (i.e. coming from the pdf) then the b has to be massless.
If the b is massless then he should not couple to the Higgs.

At leading order, this is not a real problem. You can make the computation in the unitary gauge where you can define independently the pole mass and the yukawa mass.
At next-to-leading order , this is much more complicated since you have problem with the renormalization. I know that in some situation (like 2HDM) it is possible to renormalize the model in a way to keep the hbb~ finite when the bottom mass is set to zero.
This require a specific model with a specific renormalization scheme. This can be (in principle) be handle by FeynRules but I do not know the exact status on this. (I know that the 2HDM case is under validation for the moment).

For more information on this, you can contact Celine Degrande. But she is currently on maternity leave, so it might take a while to get an answer.

>With
>loop_sm-no_mass
>or so,
>"Born diagrams could not be generated"

This is because the b being massless does not couple to the Higgs. So you do not have any diagram for your process.

>With loop_sm
>or so,
>"Fatal error in set_tau_min"

This is because at NLO we can not handle massive initial state.

Cheers,

Olivier

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