Is colour flow considered in MadGraph cross-section calculations

Hi,

The interference is correctly computed as long as you define (1) and (2) in a single “generate” line.
Doing “genenerate (1);add process (2)” will not include any interference.

Cheers,

Didier

> On 16 Feb 2017, at 14:47, Didier Alexandre <email address hidden> wrote:
>
> New question #463065 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/463065
>
> Dear experts,
>
> I am currently doing an interference study between single heavy top (T, from the VLQ_UFO model) and W+jets events using MadGraph. In the 5f scheme interference could for instance occur between the following processes:
>
> (1) ub->dT, T->w+b
> (2) ub->bdw+
>
> where (1) is mediated via a w+, and (2) via a gd-fusion. [I can send the Feynman diagrams by email]
>
> These processes will however only interfere in the cases in which the colour flow is the same, e.g.. :
>
> (1) u(r)b(r)->d(r)T, T->w+b(r)
> (2) u(r)b(r)->b(r)d(r)w+
>
> and the same would work for (b) and (g) colours. Since (2) is mediated via a gluon, the number of degrees of freedom for colour exchange is bigger than in (1), and therefore the interference is suppressed.
>
> My question is whether MadGraph takes the colour flow into account, and thus does not exaggerate the interference effect.
>
> Many thanks in advance,
> Didier
>
> --
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Hi,

Thanks, indeed that is how I proceed. I was just wondering about whether the colour flow is considered in the computation of the effect.

Thanks a lot for the answer. This problem is solved then.
Didier