CalcHEP

4 colour vertex

Asked by Safinaz

Dear authors,

I try to implement 4 colour vertex to Calchep using
FeynRules : S S G G .. where S are octet scalars, but
It says try to implement this vertex to calchep by hand,
I tried to add the vertex to the lgr.mdl file but the
Lorentz part calchep gives error about it. . So what
Should I add this part ..

Regards,
Safinaz

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Neil Christensen (neil-christensen-qft) said : 		#1

Dear Safinaz,

You need to split the vertex using an auxiliary field. Unfortunately, at this time, FeynRules does not do this for you except in a few special cases. See the end of Section 8.4 of http://arxiv.org/pdf/1207.6082.pdf for further information.

Best wishes,
Neil

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Safinaz (sramadan) said : 		#2

Hi Dr. Neil,

So the 4-Gluon vertex is aleardy implemented in sm-model in Calchep .. from G G G.t vertex ..
why when I say G G -> G G , it gives only 3-vertices diagrams, s and t-channels .

Regards,
Safinaz

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Alexander Belyaev (alexander.belyaev) said : 		#3

Dear Safinas,
you can use LanHEP to implement the vertex you want.
Details on auxilary .t field , G.t, for example is in our Manual/Write up as well is in my lectures.
All, there (in Manual/Write up and im my lectures) you can find details on 4-gluon vertex
My lectures:
http://www.personal.soton.ac.uk/ab1u06/webpage/hep_tools.htm

and particular lecture I mean is here
https://www.dropbox.com/sh/9mif11zxgl2kpvl/uidCTA4gLD/lectures/nextphd_2013/lecture2.pdf
(see page 110-112)
Cheers,
     Sasha

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Alexander Belyaev (alexander.belyaev) said : 		#4

Dear Safinaz,
what is the status of your 4-gluon question/problem?
I hope we have clarified it.
Cheers,
        Sasha

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