Triple Higgs coupling

Asked by Nikhil Bachhawat


In the restricitons on matrix elements section, there is a method given to restrict triple higgs coupllings.

^c1:c2:c3[H,H,H] and described as "exclude all triple Higgs couplings with ci constants".

So, I wanted to use this to restrict only triple higgs coupling in the process e1, E1=>H,H,Z. My code looks like this at the moment:

alias q = b
alias Q = B
process proc_3h = e1, E1 => H, H, Z {$restrictions = "1+2 ~ Z && !A && ^0:0:0[H,H,H]"}
$restrictions = "^0:0:0[H,H,H]"
process proc_hbb = H => q, Q
unstable H (proc_hbb)

sqrts = 600 GeV

luminosity = 1e4
$sample = "eventfile"
sample_format = lhef
?vis_channels = true

simulate (proc_3h)

 This method did not work. Could you please give an example on how to use this restriction or a more detailed explanation of what c1, c2 and c3 are and whether I need to change the "[H,H,H]" part?

Thanks in advance,

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Nikhil Bachhawat (nikhilb1997) said :


I think I figured it out.

Using just $restrictions="^[H,H,H]" worked.

I am still leaving the question open to make sure this is correct and c1, c2 and c3 don't have to be provided.

Also if this is the case, I think a note in the manual would be helpful as the c1,c2,c3 part in the manual made it seem to me that it must be included in the code!


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Best Juergen Reuter (j.r.reuter) said :

Hi Nikhil,
the solution you found excludes all vertices with the field content [H,H,H]. In the SM (that you considered) there is only one, but e.g. in SMEFT there are more with different tensor structures. If there are e.g. three different ones with coupling constants gh3a, gh3b, and gh3c, you can exclude one specific of them by ^gh3a[H,H,H] or two of them by ^gh3a:gh3b[H,H,H]. ^[H,H,H] would exclude all three of them.

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Juergen Reuter (j.r.reuter) said :

Of course, the manual can always be clearer, but its never possible to find a formulation that is clear to everyone.

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Nikhil Bachhawat (nikhilb1997) said :

Hi Juergen,

Thanks for the reply and now realizing that c1, c2 and c3 can be replaced by other constants such as gh3a in models other than SM as you mentioned, makes the way it is written in the manual make more sense! But knowing that they might not be written at all for SM instead of zeros was the only thing that I didn't realize and only trial and error led me there.
Of course, as you say its hard to find a the perfect manual formulation and I do think you've done a great job :)

Thanks again,

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Nikhil Bachhawat (nikhilb1997) said :

Thanks Juergen Reuter, that solved my question.