BSM Interaction Order

[MikeJBaker]

Hi,

Sorry if this is a trivial question, but I couldn't find the answer in the documentation anywhere.

How do I define the interaction order for a new physics coupling?

I have written a model file for a BSM model in SARAH and all seems well. However, when I make the UFO files (for use with MG5), vertices.py has

V_70 = Vertex(name = 'V_70',
particles = [P.u1bar, P.N, P.etp],
color = ['Identity(1,3)'],
lorentz = [L.FFS1],
couplings = {(0,0):C.GC_98})

where N and etp are my new particles which couple to the up quark, and coupings.py has

GC_98 = Coupling(name = 'GC_98',
value = '1*complex(0,1)*(Yn1*complexconjugate(ZUR11) + Yn2*complexconjugate(ZUR12) + Yn3*complexconjugate(ZUR13))',
order = {'QED':1} )

I would like to be able to distinguish between QED and BSM couplings in MG5. Is there a way to have SARAH write

GC_98 = Coupling(name = 'GC_98',
value = '1*complex(0,1)*(Yn1*complexconjugate(ZUR11) + Yn2*complexconjugate(ZUR12) + Yn3*complexconjugate(ZUR13))',
order = {'BSM':1} )

?

Many thanks,

Michael Baker

[FStaub]

Hi,

that option didn't exist until now. I quickly tried to add it, see the file attached. You should be able to use now

Code: Select all

MakeUFO[BSMcouplings->{Yn}];

Only the couplings_orders.py needs to be edited by hand.

Please let me know if that works.

Cheers,
Florian

[MikeJBaker]

Hi Florian,

Many thanks for your fast response! Yes, that seems to work!

Just a word of warning for anyone else who wants to do this: I first imported the model into MG5_aMC, and then added

Code: Select all

BSM = CouplingOrder(name = 'BSM',
                    expansion_order = 99,
                    hierarchy = 1)

to coupling_orders.py. This led to the error

Code: Select all

MG5_aMC>generate p p > sq sq
INFO: Checking for minimal orders which gives processes. 
INFO: Please specify coupling orders to bypass this step. 
Command "generate p p > sq sq" interrupted with error:
KeyError : 'BSM'
Please report this bug on https://bugs.launchpad.net/mg5amcnlo
More information is found in 'MG5_debug'.
Please attach this file to your report.

The correct order is to first add the line to coupling_orders.py and then import the model for the first time. Alternatively, you can delete model.pkl and re-import the model.

Other than that, no problems so far!

Many thanks,

Mike

[FStaub]

Hi,

thank you for the feedback.

Cheers,
Florian