Four Fermion Operator: Incoherent incoming and outgoing fermion flow

Hi Maikel,

The current bottleneck for four fermion interactions is precisely how
to treat the interaction in presence of identical fermion in the
interaction.
We are currently working with Celine Degrande and Claude Duhr (author
of FR) in order to reach an agreement on how we are dealing with
identical fermion
in FR/UFO/ALOHA/MG5.

So this is indeed a missing feature.

At current stage, the safe way is to split the four fermion
interactions to two three points interactions (by adding a additional
heavy particles)

Cheers,

Olivier

On 25-juin-12, at 11:01, Maikel de Vries wrote:

> New question #201413 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/201413
>
> Hello,
>
> I get the following error:
>
> Error detected in sub-command import model /home/maikel/Physics/
> collider/topcc/mg_tcc_bsm
> write debug file MG5_debug
> If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
> InvalidModel : Fermion Flow error for interactions t~, t, t~, t:
> FFFF7: Gamma(-1,2,3)*Gamma(-1,4,1)
> Not coherent Incoming/outcoming fermion flow
>
> when trying to import a UFO file generated by FeynRules with the
> following commands:
>
> WriteUFO[LSM, Ltttt, Output -> "mg_tcc_bsm"]
> Ltttt := gBSM/(mBSM^2) tbar.Ga[mu].t tbar.Ga[mu].t;
>
> If one instead takes the fermions not to be equal, e.g.:
>
> Lddtt := gBSM/(mBSM^2) dbar.Ga[mu].d tbar.Ga[mu].t;
>
> then MadGraph is able to import the model and also do some(maybe
> all) analysis. Is this a bug or just a missing feature, cause I am
> aware of the fact that four fermion operators are still experimental.
>
> Thanks in advance,
>
> Maikel
>
> P.S. Not coherent should read incoherent, but that's just of minor
> importance.
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Thank you for your answer.

Is there any time frame for resolving this issue?

Best, Maikel

Hi Maikel,

We need it for some of our study so this should be in a reasonable
time frame, but such type of project since it evolves a lot of pieces
takes usually quite long.
The optimistic time frame will be august and the pessimistic one might
be november (after the FR/MG school in Brazil)

Cheers,

Olivier

On Jun 26, 2012, at 2:11 AM, Maikel de Vries wrote:

> Question #201413 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/201413
>
> Maikel de Vries posted a new comment:
> Thank you for your answer.
>
> Is there any time frame for resolving this issue?
>
> Best, Maikel
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.