Comment 6 for bug 1807699

Hi,

Let me be more precise, you do not need to have all three point to be zero.
But to not have the (vanishing) three points in the generated Feynman Diagram.

The restriction card should do exactly that job (remove all the vanishing three point interaction)
and leaving only a set of non vanishing three point (that madevent can integrate) or leaving only
four point interaction (That should be ok as well)

If that does not work, I would need your model to understand why.

Cheers,

Olivier

> On 12 Dec 2018, at 10:11, Peter Galler <email address hidden> wrote:
>
> Hi Olivier,
>
> thanks for your quick answer.
> As I understand this is an inherent problem of the phase space integrator. I'm afraid that the "solution [...] to simplify the model to avoid to have ANY three-point Feynman diagram" is only viable using restrictions if one also removes all SM interactions from the SMEFT. I tried naively setting as, Gf and aEW to zero but that didn't work because these parameters are used to calculate others which then causes "division by zero". Hence, it seems to me one would have to generate an entirely new UFO file using FeynRules where the Lagrangian contains only the four-fermion interaction of interest. The other option is of course to go via |dim6|^2 = |sm+dim6|^2 - |sm|^2 - 2Re(sm*dim6cc). Now I just have to find out what is more practical for me.
>
> Thanks, Olivier, for your help.
>
> Best wishes,
> Peter
>
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> MadGraph5_aMC@NLO.
> https://bugs.launchpad.net/bugs/1807699
>
> Title:
> problem with "==" notation for 4-fermion couplings in SMEFT
>
> Status in MadGraph5_aMC@NLO:
> Won't Fix
>
> Bug description:
> Dear MadGraph Team,
>
> I encountered an error that I can't resolve
> while generating s-channel single top
> in the SMEFT using only the dimension-six
> squared term (NP==1). Specifically I ran
> the following:
>
> inside the interactive MG environment:
>
> import model SMEFTsim_A_general_alphaScheme_UFO_v2
> generate u d~ > t b~ / a h z NP==1
> output single_top_schannel
>
> in the command line shell (outside of MG):
>
> I set all Wilson coefficients to zero except for
> cqq3Abs1133 using the following commands:
>
> sed -i 's/1\.000000e+00/0\.000000e+00/' single_top_schannel/Cards/param_card.dat
> sed -i '/cqq3Abs1133/ s/0\.000000e+00/1\.000000e+00/' single_top_schannel/Cards/param_card.dat
>
> Then I ran:
>
> ./single_top_schannel/bin/generate_events -f
>
> The following output appears:
>
>
> Generating 10000 events with run name run_01
> survey run_01
> INFO: compile directory
> compile Source Directory
> Using random number seed offset = 21
> INFO: Running Survey
> Creating Jobs
> Working on SubProcesses
> INFO: P1_udx_tbx
> INFO: Idle: 1, Running: 0, Completed: 0 [ current time: 12h19 ]
> STOP 1
> rm: cannot remove ‘results.dat’: No such file or directory
> ERROR DETECTED
> INFO: Idle: 0, Running: 0, Completed: 1 [ 0.12s ]
> INFO: Idle: 0, Running: 0, Completed: 1 [ 0.12s ]
> INFO: End survey
> refine 10000
> Creating Jobs
> INFO: Refine results to 10000
> INFO: Generating 10000.0 unweigthed events.
> Error when reading single_top_schannel/SubProcesses/P1_udx_tbx/G1.2/results.dat
> Command "generate_events -f" interrupted with error:
> ValueError : need more than 5 values to unpack
> Please report this bug on https://bugs.launchpad.net/mg5amcnlo
> More information is found in single_top_schannel/run_01_tag_1_debug.log'.
> Please attach this file to your report.
> quit
> INFO:
>
>
> I'm attaching the log file "run_01_tag_1_debug.log" as well as the log file
> "single_top_schannel/SubProcesses/P1_udx_tbx/G1.2/log.txt". In the second
> log file you can find the error message:
> "Problem in the multi-channeling. All amp2 are zero but not the total matrix-element"
> It seems as if this message is generated by the "DiscreteSampler module" written
> by "Valentin Hirschi" so he might be the appropriate person to forward this
> bug report to.
>
> I'm using MadGraph5_aMC@NLO version 2.6.4 on Ubuntu 14.04.
>
> I might add that this error seems to occur for 4-fermion operators only.
> The "NP==1" notation also does not work for example for cqq1Abs1331 but it does
> work for example for cuWAbs3x3. Generating the whole matrix element (sm + sm*eft + eft^2)
> works for both 4-fermion and non-4-fermion operators.
>
> Thanks, Peter
>
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