use energy dependent alpha_s in user define propagator

Asked by Chang Jung on 2020-01-13

Dear Sir,

I'm writing to ask is it possible to use energy dependent alpha_s in user define propagator?

I want to implement effective propagator with loop effect. Thanks.

Best,
Jung

Question information

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MadGraph5_aMC@NLO Edit question
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Solved by:
Chang Jung
Solved:
2020-01-13
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2020-01-13
Last reply:
2020-01-13

This question was reopened

Hi,

If we keep a pure MG5aMC context, then it should certainly be possible.
Various method for Form-Factors should be possible in this case:
https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FormFactors <https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FormFactors>

In this case, I would use the Fortran method describe in the link above.
But in this case, you can use the builtin function of MG5aMC
ALPHAS(Q)

Cheers,

Olivier

> On 13 Jan 2020, at 05:46, Chang Jung <email address hidden> wrote:
>
> New question #687950 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/687950
>
> Dear Sir,
>
> I'm writing to ask is it possible to use energy dependent alpha_s in user define propagator?
>
> I want to implement effective propagator with loop effect. Thanks.
>
> Best,
> Jung
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Chang Jung (lovejesus99wwjd) said : #2

Thanks Olivier Mattelaer, that solved my question.

Chang Jung (lovejesus99wwjd) said : #3

Dear Olivier,

Thanks for the reply, I got it.

May I ask is it possible to add unit step function in the propagator?

Thanks.

Best,
Jung

Chang Jung (lovejesus99wwjd) said : #4

Dear Olivier,

I found the theta function is the function_library.py.

When I try to use ALPHAS(Q) in the propagator.py, I got the following error (I post part of it) :
VVS6PS11_3.f:52:25:

            FCT1 = ALPHAS(MDL_Q)
                              1
     Error: Symbol ‘mdl_q’ at (1) has no IMPLICIT type
     <builtin>: recipe for target 'VVS6PS11_3.o' failed
     make[1]: *** [VVS6PS11_3.o] Error 1

May I ask do I need to import some function in propagator.py to use the ALPHAS(Q)?

Thanks.

Best,
Jung

Chang Jung (lovejesus99wwjd) said : #5

Dear Olivier,

I changed the Q into P('mu', id) * P('mu', id) then it works.

Thanks.

Best,
Jung

Hi,

You can use the following in principle:
if (P(-1,1)**2>200) then 0 else 1

Cheers,

Olivier

> On 13 Jan 2020, at 08:03, Chang Jung <email address hidden> wrote:
>
> Question #687950 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/687950
>
> Chang Jung posted a new comment:
> Dear Olivier,
>
> Thanks for the reply, I got it.
>
> May I ask is it possible to add unit step function in the propagator?
>
> Thanks.
>
> Best,
> Jung
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi,

You can use the following in principle:
if (P(-1,1)**2>200) then 0 else 1

Cheers,

Olivier

> On 13 Jan 2020, at 08:03, Chang Jung <email address hidden> wrote:
>
> Question #687950 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/687950
>
> Chang Jung posted a new comment:
> Dear Olivier,
>
> Thanks for the reply, I got it.
>
> May I ask is it possible to add unit step function in the propagator?
>
> Thanks.
>
> Best,
> Jung
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Chang Jung (lovejesus99wwjd) said : #8

Dear Olivier,

Thanks for the reply, I got it.

Best,
Jung