# form factor with anomalous couplings

Dear authors,

As long as we want to review, we want to add form factor in MG5. Therefore, we also looked at the old answers on your platform. Here, we saw your form factor statement below in your correspondence with a user. The question we want to ask you is, shouldn't P(-1,1)*P(-1,2) expression written here have a factor of 2 in front of it? So the expression should be 2*P(-1,1)*P(-1,2)

Thank you,

Best Regards.

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 Revision history for this message Olivier Mattelaer (olivier-mattelaer) said on 2021-11-16: #1

HI,

I guess you forget to include some section in your question.

Cheers,

Olivier

 Revision history for this message Ribella (ribella) said on 2021-11-16: #2

Dear Oliver,

I apologize to you. I forgot to add the question. My question is: I want to add form factor to MG5 due to unitaryness to nominal couplings for 2->3 process in linear colliders. As long as we want to review, we want to add form factor in MG5. Therefore, we also looked at the old answers on your platform. Here, we saw your form factor statement below in your correspondence with a user. The question we want to ask you is, shouldn't P(-1,1)*P(-1,2) expression written here have a factor of 2 in front of it? So the expression should be 2*P(-1,1)*P(-1,2)

Thank you,

Best Regards.

 Revision history for this message Olivier Mattelaer (olivier-mattelaer) said on 2021-11-16: #3

Hi,

Can you put the link to the other conversation? or copy that comment here?
Both expression are in a way valid and depend of the theoretical formula that you want to put.
(and also to your definition of the coupling)

Cheers,

Olivier

 Revision history for this message Ribella (ribella) said on 2021-11-16: #4

Hi,

I am given the expression as follows

In the ee-> WG process (Here G is the photon) , we will examine the WWG coupling. We want to include the form factor in this review.

Best Regards

 Revision history for this message Olivier Mattelaer (olivier-mattelaer) said on 2021-11-16: #5

So in that thread they want to use
ffvalue=(1./(1.+MAA/ffmassscale**2))**ffexponent

so in that case, I do not see any reasy to have either
2*P(-1,1)*P(-1,2) or P(-1,1)*P(-1,2)

I guess you want to use 2*P(-1,1)*P(-1,2) to be shat, but here the "P" are ordered as in the vertex and are not the momenta of the full event. If you look at the documentation, you might find (I hope) a way to get sqrts which is sqrt(shat).

Cheers,

Olivier

 Revision history for this message Ribella (ribella) said on 2021-11-17: #6

Hi,

Thank you for your answer. We don't know exactly which expression to use for the Shat center of mass energy. Do you have a document you would recommend?

Best Regards,

 Revision history for this message Olivier Mattelaer (olivier-mattelaer) said on 2021-11-17: #7

Since UFO is a local theory.
You need to break UFO and use the fortran way where you can include those (madgraph and LO specific) line

include '../maxparticles.inc'
c put momenta in common block for couplings.f
double precision pp(0:3,max_particles)
common /momenta_pp/pp

and from that full event you can re-construct any non local information that you want.

Cheers,

Olivier

> On 17 Nov 2021, at 06:16, Ribella <email address hidden> wrote:
>
> Question #699515 on MadGraph5_aMC@NLO changed:
>
>
> Ribella is still having a problem:
> Hi,
>
> Thank you for your answer. We don't know exactly which expression to use
> for the Shat center of mass energy. Do you have a document you would
> recommend?
>
> Best Regards,
>
> --