negative cross-section in processes with goldstino

Sorry,
I'll look during this weekend.
Alexander Pukhov

On 05/08/2016 04:47 PM, IvanSobolev wrote:
> Question #293315 on CalcHEP changed:
> https://answers.launchpad.net/calchep/+question/293315
>
> Description changed to:
> Dear CaclHEP team,
>
> I'm trying to calculate cross-section for a process G,G -> ~g,~Gg where G is gluon ~g is gluino and ~Gg is goldstino.
> A vertice with goldstino, gluino and gluon is written in eq.(7) in http://arxiv.org/pdf/hep-ph/0111291v1.pdf while vertice with 2goldstinos, gluino and gluon is written in eq.(6).
>
> Defenition of goldstino field and vertices are defined in "basic MSSM
> plus gravitino and sgoldstino" package from
> http://theory.sinp.msu.ru/~semenov/mssm.html
>
> I obtain negative cross-section with rather small error in both gauges.
> Do you have any idea what it can be?
>
> Cheers,
> Ivan
>

I don't see problem.
Model is attached.
Cross section is positive.

Best
     Alexander Pukhov

On 05/16/2016 12:07 PM, IvanSobolev wrote:
> Question #293315 on CalcHEP changed:
> https://answers.launchpad.net/calchep/+question/293315
>
> Description changed to:
> Dear CaclHEP team,
>
> I'm trying to calculate cross-section for a process G,G -> ~g,~Gg where G is gluon ~g is gluino and ~Gg is goldstino.
> A vertice with goldstino, gluino and gluon is written in eq.(7) in http://arxiv.org/pdf/hep-ph/0111291v1.pdf
>
> Defenition of goldstino field and vertices are defined in "basic MSSM
> plus gravitino and sgoldstino" package from
> http://theory.sinp.msu.ru/~semenov/mssm.html
>
> I obtain negative cross-section with rather small error in both gauges.
> Do you have any idea what it can be?
>
> Cheers,
> Ivan
>
> UPD: I removed the following statement "...while vertice with
> 2goldstinos, gluino and gluon is written in eq.(6)..." since it is not
> correct.
>

Thanks a lot for you answer!

But could you please attach model files you're using?
Because as for me I get negative cross-section for mentioned process. But what is strange I get positive result of G,~G->G,~g and G,~g->G,~G processes.

Here's a screenshot of what I get. Do you have the same diagrams?
http://s32.postimg.org/wu00t7ac5/screen.jpg

Cheers,
Ivan

I have attached the model to my previous mail.
It seems launchpad does not resend attachment.
OK, find it here
     http://theory.sinp.msu.ru/~pukhov/m9.tgz
I just take model from site of Andrey Semenov but save only vertex
relative to your process.

Best
     Alexander Pukhov

On 05/16/2016 06:07 PM, IvanSobolev wrote:
> Question #293315 on CalcHEP changed:
> https://answers.launchpad.net/calchep/+question/293315
>
> Status: Answered => Open
>
> IvanSobolev is still having a problem:
> Thanks a lot for you answer!
>
> But could you please attach model files you're using?
> Because as for me I get negative cross-section for mentioned process. But what is strange I get positive result of G,~G->G,~g and G,~g->G,~G processes.
>
> Here's a screenshot of what I get. Do you have the same diagrams?
> http://s32.postimg.org/wu00t7ac5/screen.jpg
>
> Cheers,
> Ivan
>

Thanks a lot for your answer!

But why didn't you include G | G | G | vertice? The answer changes drastically when you try to include it...
Actually it becomes negative.

Best,
Ivan

I have implemented a part you asked me about.
Try to change a sign at G (3/2)(3/2) term. It should help.

I'll try to prepare example of 3/2 interaction in CalcHEP.

Best
    Alexander Pukhov

On 06/08/2016 02:22 PM, IvanSobolev wrote:
> Question #293315 on CalcHEP changed:
> https://answers.launchpad.net/calchep/+question/293315
>
> Status: Answered => Open
>
> IvanSobolev is still having a problem:
> Thanks a lot for your answer!
>
> But why didn't you include G | G | G | vertice? The answer changes drastically when you try to include it...
> Actually it becomes negative.
>
> Best,
> Ivan
>

Sorry, I don't really understand which term do you mean? (G (3/2) (3/2))
Do you mean gluon-goldstino-goldstino vertice? I mean, I don't see it...

Best,
Ivan

Dear Ivan. I really nether see Andrei Semenov paper/model. I have
copied for you a part of it without looking inside.
Now I try to implement in CalcHEP spin 3/2 according to
*arXiv:1208.5811. <http://arXiv.org/abs/arXiv:1208.5811>
*Here I collaborate with Kyiungchul Kong. Not all points are clear for
us in spite we have a very good agreement with results of paper and
results obtained by Madgraph almost for all channels. To get agreement
I have changes a sign at (G (3/2) (3/2)).
I still don't understand this puzzle. It seems, propagator of spin
(3/2) in CalcHEP has a sign different from one presented in the papers.
So, free lagrangian also should have an opposite sign as well as **(G
(3/2) (3/2)) vertex. From the other side I can not change sing of
propagator keeping width of (3/2) positive. I propose you to change
sing at **(G (3/2) (3/2)) . From the other side, may be you have
negative result because you don't apply cuts for energies of gluon and
   and separation angle between gluons. Infrared and co-linear
divergences can get negative points even in case of correct Lagrangian.
I hope in couple of days I will know answer of your and my questions
about 3/2

Best
   Alexander Pukhov

On 06/20/2016 05:12 PM, IvanSobolev wrote:
> Question #293315 on CalcHEP changed:
> https://answers.launchpad.net/calchep/+question/293315
>
> Status: Answered => Open
>
> IvanSobolev is still having a problem:
> Sorry, I don't really understand which term do you mean? (G (3/2) (3/2))
> Do you mean gluon-goldstino-goldstino vertice? I mean, I don't see it...
>
> Best,
> Ivan
>

Seems like I found a mistake and now I get positive cross-section. But I faced another problem. When I calculate cross-sections in CompHEP and CalcHEP using exactly the same files (up to some not relevant changes according to CaclHEP interface) I get different values though the squared matrix elements are exactly the same. The difference is not that big (actually they differ by a factor of ~1.5 or something) but still it's confusing. Which results should I trust? Can I send you the model files I use via e-mail?

Best,
Ivan

Thanks Alexander Pukhov, that solved my question.