Virtual particle in outer leg

Asked by Sayan Dasgupta on 2020-09-25

Hello,

I am trying to generate a process "p p > t > w+ b t~". This is to keep the top virtual and use it's propagator and not decay it on shell. Will this work? I am getting different values of cross-section when I specify "propagator=Prop.F" in the UFO under top and when I don't specify anything.

Thanks in advance.

Regards,
Sayan.

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2020-10-01
Last query:
2020-10-01
Last reply:
2020-09-28

What is the definition of Prop.F?

Cheers,

Olivier

Sayan Dasgupta (sayandg) said : #2

Hello Olivier,

It points to the usual fermionic propagator defined in propagators.py file in the UFO.

Regards,
Sayan.

Which is? (This depend of the method that you use to generate that file and the version of the tools that you use)
Since those information are not used by default, many code have the wrong propagator by default.
So it might be the issue.

Olivier

Sayan Dasgupta (sayandg) said : #4

I have generated the UFO from the latest version of Feynrules.

The propagator F as defined in the file propagators.py is

denominator = "P('mu', id) * P('mu', id) - Mass(id) * Mass(id) + complex(0,1) * Mass(id) * Width(id)"

F = Propagator(name = "F",
                numerator = "complex(0,1) * (Gamma('mu', 1, 2) * P('mu', id) + Mass(id) * Identity(1, 2))",
                denominator = denominator
               )

Regards,
Sayan.

The correct one is:

F = Propagator(name = "F",
                numerator = "(Gamma('mu', 1, 2) * \
                    P('mu', id) + Mass(id) * Identity(1, 2))",
                denominator = denominator
               )

Cheers,

Olivier

> On 25 Sep 2020, at 09:05, Sayan Dasgupta <email address hidden> wrote:
>
> Question #693086 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/693086
>
> Status: Answered => Open
>
> Sayan Dasgupta is still having a problem:
> I have generated the UFO from the latest version of Feynrules.
>
> The propagator F as defined in the file propagators.py is
>
> denominator = "P('mu', id) * P('mu', id) - Mass(id) * Mass(id) +
> complex(0,1) * Mass(id) * Width(id)"
>
> F = Propagator(name = "F",
> numerator = "complex(0,1) * (Gamma('mu', 1, 2) * P('mu', id) + Mass(id) * Identity(1, 2))",
> denominator = denominator
> )
>
> Regards,
> Sayan.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Sayan Dasgupta (sayandg) said : #6

Thanks Olivier, that solved my problem. Can you please tell me why Feynrules generates such wrong propagators?

Regards,
Sayan.

Sayan Dasgupta (sayandg) said : #7

Thanks Olivier Mattelaer, that solved my question.

Can not comment for the FeynRules author.

Cheers,

Olivier

> On 1 Oct 2020, at 08:15, Sayan Dasgupta <email address hidden> wrote:
>
> Question #693086 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/693086
>
> Status: Answered => Solved
>
> Sayan Dasgupta confirmed that the question is solved:
> Thanks Olivier, that solved my problem. Can you please tell me why
> Feynrules generates such wrong propagators?
>
> Regards,
> Sayan.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Sayan Dasgupta (sayandg) said : #9

Ok thank you.

Regards,
Sayan.