Error in computation of bpower

Asked by Baptiste Ravina on 2020-09-11

Dear experts,

I am using the SMEFT@NLO model available here: http://feynrules.irmp.ucl.ac.be/wiki/SMEFTatNLO

In version 2.7.3, I first import the model with a restriction card
> import model SMEFTatNLO-NLO

then try to generate a simple ttbar process
> generate p p > t t~ QCD=2 QED=0 NP=2 [QCD]
(note that this example is given in the wiki above)

Computation is interrupted due to multiple occurrences of
"Error in computation of bpower:
  not an integer 1.9999975547352327"

Is this a known issue?
Cheers,
Baptiste

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Eleni Vryonidou Edit question
Solved by:
Baptiste Ravina
Solved:
2020-09-12
Last query:
2020-09-12
Last reply:
2020-09-12

Did you see this comment in the link that you point:

> The 3.0.3-neworders development branch (‚Äčtarball <https://bazaar.launchpad.net/~maddevelopers/mg5amcnlo/3.0.3-neworders/tarball>) of MG is required for NLO predictions involving four-fermion operators and (in general) H2G2 with coefficient cpG not normalized with any power of gS. It also allows for a better control over coupling orders and, in particular, for the separate computation of linear and quadratic EFT contributions at NLO, in fixed order mode. A branch allowing for the separate computation of different orders in event-generation mode (with matching to parton shower) is being validated. The 2.X.X series of MadGraph5_aMC@NLO can handle bosonic and two-fermion operators at one-loop.

Cheers,

Olivier

> On 11 Sep 2020, at 18:15, Baptiste Ravina <email address hidden> wrote:
>
> New question #692868 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/692868
>
> Dear experts,
>
> I am using the SMEFT@NLO model available here: http://feynrules.irmp.ucl.ac.be/wiki/SMEFTatNLO
>
> In version 2.7.3, I first import the model with a restriction card
>> import model SMEFTatNLO-NLO
>
> then try to generate a simple ttbar process
>> generate p p > t t~ QCD=2 QED=0 NP=2 [QCD]
> (note that this example is given in the wiki above)
>
> Computation is interrupted due to multiple occurrences of
> "Error in computation of bpower:
> not an integer 1.9999975547352327"
>
> Is this a known issue?
> Cheers,
> Baptiste
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Baptiste Ravina (bravina) said : #2

Hi Olivier,

Yes I did see that. According to that last sentence, I would expect 2.7.3 to work if I my only non-zero operator is ctG? Maybe there's something else I should be doing with the restriction card? Should I comment out the four-fermion operators rather than setting them to zero/epsilon?

Cheers,
Baptiste

I'm not an author of that model, so I can not comment on that.
I have assign the question to one author of the model, but they are no assurance that they will answer to the question asked here.

Cheers,

Olivier

Baptiste Ravina (bravina) said : #4

Hi Olivier,

I followed up with one of the authors and it seems I do need to set those four-fermion operators to exactly zero (rather than small values as per the twiki recommendation, or commented out). I'll mark this question as answered then :)

Thanks,
Baptiste