Change Higgs couplings for loop_sm

Asked by Ans on 2020-03-05

Dear Experts,

I need to to change Higgs couplings universally in a way to mimic Higgs 'signal strength' changes for a kappa framework measurement. It is for the off-shell Higgs to 4 leptons analysis so the loops are important.

For the sm model I added a new internal parameter "rssH" to the FeynRules model that multiplies to each term where yu, yd, and yl show up and generated a UFO. Then multiplied the same parameter to the Higgs to VV couplings in the file like:

GC_50 = Coupling(name = 'GC_50',
                 #value = '(ee**2*complex(0,1)*vev)/(2.*sw**2)',
                 value = 'rssH*((ee**2*complex(0,1)*vev)/(2.*sw**2))',
                 order = {'QED':1})

GC_59 = Coupling(name = 'GC_59',
                 #value = 'ee**2*complex(0,1)*vev + (cw**2*ee**2*complex(0,1)*vev)/(2.*sw**2) + (ee**2*complex(0,1)*sw**2*vev)/(2.*cw**2)',
                 value = 'rssH*(ee**2*complex(0,1)*vev + (cw**2*ee**2*complex(0,1)*vev)/(2.*sw**2) + (ee**2*complex(0,1)*sw**2*vev)/(2.*cw**2))',
                 order = {'QED':1})

However to simulate offshell gg(H)zz to 4 leptons I think I need loop_sm. How can I make the equivalent changes for loop_sm ?

I would like to be able to produce samples where the the "signal strength" is for example 5x the standard model (even though the concept of signal strength is a bit unclear now with interference effects).

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Modifying a UFO model by hand is certainly not something simple.
Actually, I can not do such modification manually, this is too complex.

So my advice is to always use FeynRules/NLOCT for creating model.
The issue here is that you need to be careful about the renormalization condition when you modify the model.
How is your parameter renormalised?

I know that they are special cases but in general, signal strenght are not NLO compatible, so except if you are in one of the exception (I thought the only exception was the one related to the triple higgs vertex), you might not be able to do it.
In that case, the solution should be to use EFT theories.



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