Generation of events for QED loop process possible?

Hi,

We can handle loop induced processes for QED like loop but nothing more.

So for your process, we can do it via the syntax:
> generate a a > a a [noborn=QED]

> Ultimately the goal is to add a scalar particle which directly couples to photons (axion - like particle), and events for this should be generated as well. Are there any obstacles expected when trying this?

But then this is a tree-level contribution which can not be computed simultaneously as a loop-induced processes.

Cheers,

Oliver

> On 9 Jun 2017, at 19:09, Kristof Schmieden <email address hidden> wrote:
>
> New question #642775 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/642775
>
> Hello,
>
> I'm trying to use MG5_aMC_v2_5_5 to generate the photon scattering loop diagram.
> I tried using the model loop_qcd_qed_sm with the command:
> generate a a > a a [virt=QED]
>
> However in this case only one phase space point is generated. Is there a way to generate events for this process?
>
> Ultimately the goal is to add a scalar particle which directly couples to photons (axion - like particle), and events for this should be generated as well. Are there any obstacles expected when trying this?
>
> Thanks a lot for your help,
> Kristof
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Notice that if you are interested in the interference of the loop-induced
contribution to a a > a a with the tree-level one from the axion-like
particle, you can try and follow the recipe laid out on this wiki page:
https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LoopInducedTimesTree

On Fri, Jun 9, 2017 at 8:53 PM, Olivier Mattelaer <
<email address hidden>> wrote:

> Question #642775 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/642775
>
> Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> Hi,
>
> We can handle loop induced processes for QED like loop but nothing more.
>
> So for your process, we can do it via the syntax:
> > generate a a > a a [noborn=QED]
>
>
> > Ultimately the goal is to add a scalar particle which directly couples
> to photons (axion - like particle), and events for this should be generated
> as well. Are there any obstacles expected when trying this?
>
> But then this is a tree-level contribution which can not be computed
> simultaneously as a loop-induced processes.
>
> Cheers,
>
> Oliver
>
> > On 9 Jun 2017, at 19:09, Kristof Schmieden <question642775@answers.
> launchpad.net> wrote:
> >
> > New question #642775 on MadGraph5_aMC@NLO:
> > https://answers.launchpad.net/mg5amcnlo/+question/642775
> >
> > Hello,
> >
> > I'm trying to use MG5_aMC_v2_5_5 to generate the photon scattering loop
> diagram.
> > I tried using the model loop_qcd_qed_sm with the command:
> > generate a a > a a [virt=QED]
> >
> > However in this case only one phase space point is generated. Is there a
> way to generate events for this process?
> >
> > Ultimately the goal is to add a scalar particle which directly couples
> to photons (axion - like particle), and events for this should be generated
> as well. Are there any obstacles expected when trying this?
> >
> > Thanks a lot for your help,
> > Kristof
> >
> > --
> > You received this question notification because you are an answer
> > contact for MadGraph5_aMC@NLO.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.
>

--
Valentin