error in LNV process

not sure what you mean, I don't see w- > l+ N happening in your description

I'm sorry, let me describe more clearly.

The LNF process which I want to generate is : u d~ > w+ w+ > l+ l+ u~ d, because of these two same-charge leptons, there should also have same-charge bosons w+.

However in madgraph, the second boson is w-, this is clearly violated the charged conservation.

Maybe you can tell me your e-mail address and I can send you the feynman diagrams.

Dear LinYun He,

Thank you for your question regarding the charge conservation in the Feynman diagrams generated by MadGraph for your specified process. The displayed diagram showing the vertex
𝑊
−
→
𝑙
+
𝑁
W
−
 →l
+
 N indeed appears to violate charge conservation, which is not physically permissible in the Standard Model or its extensions like the Type-I seesaw model.

This issue may arise from an inconsistency in how the model parameters or interactions are implemented in the MadGraph session. I recommend the following steps to address it:

Check the Model Implementation: Ensure that the Type-I seesaw model has been correctly imported, and all interactions, including vertex rules and coupling constants, are properly defined.

Inspect the Process Syntax: Verify that the syntax used to define the process in MadGraph aligns with the conventions for charge and particle assignments.

Review the Output Files: Check the .lhe or .proc_card files generated to confirm whether the issue persists in the event generation stage.

As a general analogy, just as a well-designed nooro leg massager ensures proper alignment and functionality to deliver effective relief, a simulation tool like MadGraph requires careful parameter configuration to maintain physical consistency.

Dear Ali joe,

Thanks for your help.

I just import the typI model and try to generate the single vertex like : u d~ > W+, W+ > l+ N, it's ok and the wrong process w- > l+ N

can also received error message under this model.

However the result of process p p > w+ w+ > l+ l+ j j was still wrong because of the w- appeared and madgraph didn't show any error

message, more importantly, the feynman diagrams displayed by madgraph are all one w+ with one w-, even I use command: / w+ w-.

This model is download from CERN website and created by 'claude.duhr'. Do you think I still need to check the Process Syntax?

What is the exact name of your model?
Such that I can generate the diagram myself?

Otherwise the syntax:
p p > w+ w+ > l+ l+ j j
does not make that much sense
Since the syntax > A B >
means that you are going to filter diagram to ensure at least one propagator in S-channel of type A and at least one of type B
if you do
> A A > you ask twice for at least ONE propagator in S-channel of type A. So this is exactly the same as asking once.

Using > A > syntax (or his variant) is actually discouraged since diagram filtering can break gauge and lorentz invariance.
You should prefer the syntax for onshell decay like:
generate p p > A A, A > B C, A > C D
generate p p > A A, A > B C (which is the same as p p > A A, A > B C , A >B C)

Cheers,

Olivier

Dear Olivier Mattelaer,

Thanks for your help.

My model name is typeISeeSaw_MajNeutrino which can be download from ' https://cms-project-generators.web.cern.ch/cms-project-generators/'.

I can ues ' p p > l+ l+ j j' to creat all s-channel and t-channel, however they are all one W+ with one W-.

By the way, is there any command in madgraph that can banned x-channel directly? like / t-channel?

<email address hidden>

remove NO SPAM

Dear Sihyun Jeon, I have send a email to you, thanks for your help!

So to ban a particle to be in a S-channel: $$ X
to ban a particle to be present : / X
we can not ban T-channel

I have check your model, and it does conserve electric charge, and I do not understand which diagram you would like to have with two W+. Mabe you need another model but this one is reasonable

Cheers,

Olivier

Dear Olivier Mattelaer,

I want to generate the meson LNV decay under Type-I model, and you can check this process through this paper

'https://inspirehep.net/literature/811669', which is clearly have two W+.

Thank you for your help, and if you have some new ideas about my question, please tell me!

Hi,

The charge of a particle in T-channel is a pure point of view of the drawer.
And depend of which interaction occur first (but they are not ordered).
So in practise some of those diagram will have a w+ and some a w-.

The display of diagram of madgraph does not try to be fully consistent in the naming of such particles and just follow the ordering of the particles within the internal representation of madgraph where ordering is optimised for the speed of the computation and not for user readibility.

So yes, madgraph does have such diagram where you have two W in T-channel and l+ l+ in final state.
But you can not select such diagram with > w+ > since this syntax is for S-channel.

So such contribution is correctly handle by this model/madgraph.

Cheers,

Olivier

> On 29 Nov 2024, at 08:35, LinYunHe <email address hidden> wrote:
>
> Question #819441 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/819441
>
> Status: Answered => Open
>
> LinYunHe is still having a problem:
> Dear Olivier Mattelaer,
>
> I want to generate the meson LNV decay under Type-I model, and you can
> check this process through this paper
>
> 'https://inspirehep.net/literature/811669', which is clearly have two
> W+.
>
> Thank you for your help, and if you have some new ideas about my
> question, please tell me!
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dear Olivier Mattelaer,

Thank you. So you means that the command 'p p > l+ l+ j j ' is correct to describe the meson LNV process? even though the diagrams

from this command have two different charge W, and the meson LNV process (both t- and s-channel) has two same charge W ?

What's more, we can not select t-channel in MG5 right? So how can we only foucs on t-channel? espectially in such meson LNV process.

best,

LinYun

Dear Olivier Mattelaer,

Thank you for your help!

Thanks Olivier Mattelaer, that solved my question.