Unable to add the new physics contribution to t t~

[Disha Bhatia]

Hi,

I am trying to compute the full BSM contribution to t t~ at one loop in QCD.

I am proceeding this through the command : p p > t t~ [QCD] NEW=99 QCD=99,
however this is giving me still the contributions due to QCD, I also tried other variants, for ex NEW=2 etc
but none is working. It gives me only QCD contribution:

generate p p > t t~ / z a [QCD] NEW=2
Interpreting 'NEW=2' as 'NEW<=2'
INFO: Generating FKS-subtracted matrix elements for born process: g g > t t~ NEW<=2 [ all = QCD ] / z a (1 / 9)
INFO: Generating FKS-subtracted matrix elements for born process: u u~ > t t~ NEW<=2 [ all = QCD ] / z a (2 / 9)
INFO: Generating FKS-subtracted matrix elements for born process: c c~ > t t~ NEW<=2 [ all = QCD ] / z a (3 / 9)
INFO: Generating FKS-subtracted matrix elements for born process: d d~ > t t~ NEW<=2 [ all = QCD ] / z a (4 / 9)
INFO: Generating FKS-subtracted matrix elements for born process: s s~ > t t~ NEW<=2 [ all = QCD ] / z a (5 / 9)
INFO: Generating FKS-subtracted matrix elements for born process: u~ u > t t~ NEW<=2 [ all = QCD ] / z a (6 / 9)
INFO: Generating FKS-subtracted matrix elements for born process: c~ c > t t~ NEW<=2 [ all = QCD ] / z a (7 / 9)
INFO: Generating FKS-subtracted matrix elements for born process: d~ d > t t~ NEW<=2 [ all = QCD ] / z a (8 / 9)
INFO: Generating FKS-subtracted matrix elements for born process: s~ s > t t~ NEW<=2 [ all = QCD ] / z a (9 / 9)
INFO: Generating virtual matrix elements using MadLoop:
INFO: Generating virtual matrix element with MadLoop for process: g g > t t~ NEW=0 QCD<=2 [ all = QCD ] / z a (1 / 9)
INFO: Generating virtual matrix elements using MadLoop:
INFO: Generating virtual matrix element with MadLoop for process: u u~ > t t~ NEW=0 QCD<=2 [ all = QCD ] / z a (2 / 9)
INFO: Generating virtual matrix elements using MadLoop:
INFO: Generating virtual matrix element with MadLoop for process: c c~ > t t~ NEW=0 QCD<=2 [ all = QCD ] / z a (3 / 9)
INFO: Generating virtual matrix elements using MadLoop:
INFO: Generating virtual matrix element with MadLoop for process: d d~ > t t~ NEW=0 QCD<=2 [ all = QCD ] / z a (4 / 9)
INFO: Generating virtual matrix elements using MadLoop:
INFO: Generating virtual matrix element with MadLoop for process: s s~ > t t~ NEW=0 QCD<=2 [ all = QCD ] / z a (5 / 9)
INFO: Generating virtual matrix elements using MadLoop:
INFO: Generating virtual matrix element with MadLoop for process: u~ u > t t~ NEW=0 QCD<=2 [ all = QCD ] / z a (6 / 9)
INFO: Generating virtual matrix elements using MadLoop:
INFO: Generating virtual matrix element with MadLoop for process: c~ c > t t~ NEW=0 QCD<=2 [ all = QCD ] / z a (7 / 9)
INFO: Generating virtual matrix elements using MadLoop:
INFO: Generating virtual matrix element with MadLoop for process: d~ d > t t~ NEW=0 QCD<=2 [ all = QCD ] / z a (8 / 9)
INFO: Generating virtual matrix elements using MadLoop:
INFO: Generating virtual matrix element with MadLoop for process: s~ s > t t~ NEW=0 QCD<=2 [ all = QCD ] / z a (9 / 9)
INFO: Generated 9 subprocesses with 136 real emission diagrams, 11 born diagrams and 124 virtual diagrams

AT LO, I tried to omit and add QED contributions which happen very nicely either by using QED=2/99

But my new physics contribution exists at one loop, and I am unable to generate the events together, this is crucial for me since I need the interference terms. Can you please help me in this regard?

Thanks,
Disha

[Disha Bhatia (dishabhatia1989)]

Thanks Oliver, as per your suggestion I have made my question as a part of the bug.
I have attached the new physics diagrams which I want to add to the usual tt~ contribution from the standard model and have also attached the model file. I am currently using the madgraph version MG5_aMC_v2_6_7.

Thank you,
Disha

[Olivier Mattelaer (olivier-mattelaer)]

Hi,

The diagram that you want have a QED contribution so you do enter a mixed-expansion regime.
mixed expansion are supported only since 3.x release.
However your model is only able to do NLO in QCD and therefore is not ready for mixed expansion computation.
Independently, I do not see why you play with "NEW" since for this process it seems that only "QED" matters.

So i'm not sure what is the best way to move forward here.
One way would be to go like this (within 3.1.1):
generate p p > t t~ NEW=0 QCD<=99 QED<=99 [QCD]
(or generate p p > t t~ NEW<=2 QCD<=99 QED<=99 [QCD])

You will see a lot of warning of potential missmatch and you need to be sure that none of those serious warning (potential missing real contribution and missing loop) does affect your computation.

The second option is to hack the code to compute such intereference.
Your diagram sounds like loop-induced processes and if this is the case, then similar hack of the code have been done in the code in the past, this is not officially supported but you can find how the hack was done at this page:
https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LoopInducedTimesTree

Cheers,

Olivier

> On 11 Aug 2021, at 07:22, Disha Bhatia <email address hidden> wrote:
>
> ** Attachment added: "This are the feynman diagrams which I want to add"
> https://bugs.launchpad.net/mg5amcnlo/+bug/1939495/+attachment/5517226/+files/diagrams_0_gg_ttx_no_azgtth1h2h3.eps
>
> --
> You received this bug notification because you are subscribed to
> MadGraph5_aMC@NLO.
> https://bugs.launchpad.net/bugs/1939495
>
> Title:
> Unable to add the new physics contribution to t t~
>
> Status in MadGraph5_aMC@NLO:
> New
>
> Bug description:
> Hi,
>
> I am trying to compute the full BSM contribution to t t~ at one loop
> in QCD.
>
> I am proceeding this through the command : p p > t t~ [QCD] NEW=99 QCD=99,
> however this is giving me still the contributions due to QCD, I also tried other variants, for ex NEW=2 etc
> but none is working. It gives me only QCD contribution:
>
> generate p p > t t~ / z a [QCD] NEW=2
> Interpreting 'NEW=2' as 'NEW<=2'
> INFO: Generating FKS-subtracted matrix elements for born process: g g > t t~ NEW<=2 [ all = QCD ] / z a (1 / 9)
> INFO: Generating FKS-subtracted matrix elements for born process: u u~ > t t~ NEW<=2 [ all = QCD ] / z a (2 / 9)
> INFO: Generating FKS-subtracted matrix elements for born process: c c~ > t t~ NEW<=2 [ all = QCD ] / z a (3 / 9)
> INFO: Generating FKS-subtracted matrix elements for born process: d d~ > t t~ NEW<=2 [ all = QCD ] / z a (4 / 9)
> INFO: Generating FKS-subtracted matrix elements for born process: s s~ > t t~ NEW<=2 [ all = QCD ] / z a (5 / 9)
> INFO: Generating FKS-subtracted matrix elements for born process: u~ u > t t~ NEW<=2 [ all = QCD ] / z a (6 / 9)
> INFO: Generating FKS-subtracted matrix elements for born process: c~ c > t t~ NEW<=2 [ all = QCD ] / z a (7 / 9)
> INFO: Generating FKS-subtracted matrix elements for born process: d~ d > t t~ NEW<=2 [ all = QCD ] / z a (8 / 9)
> INFO: Generating FKS-subtracted matrix elements for born process: s~ s > t t~ NEW<=2 [ all = QCD ] / z a (9 / 9)
> INF...

[Disha Bhatia (dishabhatia1989)]

Hi,

Thanks a lot Oliver, yes this is a QED diagram, actually since this involves the new physics
interaction i.e. why in my mind it was NEW interaction.

Thanks a lot for the suggestion, I now understand that why it was not able to generate the combined terms. I will look into the hack code you suggested to calculate mixed interference terms.

Thanks a lot,
Disha