How do I change V_tb?

Asked by Roberto Franceschini on 2019-08-23

As far as I can see the most general CKM in the sm model, sm_ckm for instance, is Wolfestein hence Vtb=1.

How do I change Vtb in MG SM model?

Cheers
Roberto

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Roberto Franceschini
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2019-08-23
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2019-08-23
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2019-08-23

You need to go back to feynrules and choose yourself the ckm sector

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From: <email address hidden> <email address hidden> on behalf of Roberto Franceschini <email address hidden>
Sent: Friday, August 23, 2019 5:42:55 AM
To: Olivier Mattelaer <email address hidden>
Subject: [Question #683183]: How do I change V_tb?

New question #683183 on MadGraph5_aMC@NLO:
https://answers.launchpad.net/mg5amcnlo/+question/683183

As far as I can see the most general CKM in the sm model, sm_ckm for instance, is Wolfestein hence Vtb=1.

How do I change Vtb in MG SM model?

Cheers
Roberto

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Thanks for this message Oliver. I was thinking to make a change in parameters.py and make VCKM3x3 external, adding it to the LH block of the Wolfenstein. How does it sound?
Thanks for your input.
Roberto

I have modified parameter.py as to have an external parameter that is used to set the internal one

Vtb = Parameter(name = 'Vtb',
                nature = 'external',
                type = 'real',
                value = 1.0,
                texname = '\\text{Vtb}',
                lhablock = 'Wolfenstein',
                lhacode = [ 5 ])

CKM3x3 = Parameter(name = 'CKM3x3',
                   nature = 'internal',
                   type = 'complex',
                   value = 'Vtb',
                   texname = '\\text{CKM3x3}')

In this way I am following the same mechanism used for the other Wolfenstein parameters.

Adding the line
   5 1.000000e+00 # Vtb
in the Wolfenstein block of the restrictions.dat and in the param_card.dat makes no error pop up at generation or output step.

I have noted, but maybe is a chance of a mistake on my side, that if I do display parameters after having imported the model these parameters do not show up. However if I put something different than 1 in the defaults (both in restrictions.dat and in parameters.py) then I get the t> b w+ decay width to depend on what I put in param_card.dat