a question about lgrng1.mdl file

Asked by MohammadMohammadidoust on 2021-02-14

 Hi!

I have implemented a model in lanhep with no error. Neither lanhep nor calchep detect error.
I also used hermitian check and mass check. every thing is fine. But in the lgrng1.mdl file something looks wrong.
for some 4-particle amplitudes the factor is just a constant, However it must be a function of quartic couplings.
I don't know where this problem comes from.
if it's possible please help me to solve this problem.
I can attach the source file if it is necessary.

thanks a lot.

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Alexander Belyaev
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MohammadMohammadidoust (m23mohamadidoust) said :
#1

I think its because of a variables like B0000 and etc which lanhep automatically declares.
How could I avoid generating this variables?

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Alexander Belyaev (alexander.belyaev) said :
#2

Why do you want to avoid generation of these variables?
And why do you think lagrangian looks wrong?
B0000 etc variables are defined in func.mdl files and aimed to spead up CaclHEP performance by great deal.
What is the preoblem you are facing with?

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MohammadMohammadidoust (m23mohamadidoust) said :
#3

Hello again and thank you for your helps

In the IDM model for instance, which you have implemented it in the micromegas, in the lgrng1.mdl we can see two different 4-particle amplitude factors that it seems their factors should be the same. But they aren't:

particles factor

z.f z.f ~H+ ~H- -la3
z.f z.f ~H3 ~H3 -1

I think the scattering amplitude of these two are the same. why they are different while ~H+ , ~H- and ~H3 came from a same doublet?

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Alexander Belyaev (alexander.belyaev) said :
#4

First of all
z.f z.f ~H3 ~H3 coupling is not -1, it is -B0004 = -la3-la4-la5

Secondly, why do you think that couplings for these interactions should be the same?
Please take a look at the Lagrangian for IDM!

Take a look at one of the papers, e.g. https://arxiv.org/pdf/1612.00511.pdf Eq(2)
You can see from there that couplings for \phi_1\phi_1\phi_2\phi_2
interactions comes from THREE terms:
lam3, lam4, lam5
You can easily derive interactions even without LanHEP for these terms and see that
couplings for
z.f z.f ~H3 ~H3 and z.f z.f ~H+ ~H-
should not be the same

Alexander

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MohammadMohammadidoust (m23mohamadidoust) said :
#5

dear prof Belyaev
I expanded the lagrangian you have introduced in that paper and found there are repetitious terms for some interactions like z.f z.f ~H3 ~H3.
my question is why we avoid putting such terms repetitiously in our model ?
is it possible to have a same interaction with different couplings ?
I'm sorry because this question doesn't belong to calchep.

sincerely
Mohammad

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MohammadMohammadidoust (m23mohamadidoust) said :
#6

actually I mean why we don't avoid putting such terms?

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Best Alexander Belyaev (alexander.belyaev) said :
#7

Dear Mohammad

please look carefully at Eq(2) of https://arxiv.org/pdf/1612.00511.pdf

: terms with l3,l4 andl5 are NOT identical!

They form Lorents invariants, but ht econvolution ver SU(2) indices is DIFFERENT!!!

These are different terms and they all must be included, they correspond to THREE different ways of forming
 Lorents invariant out of phi1 and phi2 doublets and they ALL must be included

Best Alexander

P.S. I sugest you to close this question

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MohammadMohammadidoust (m23mohamadidoust) said :
#8

dear prof Bleyaev

thanks for your clarification.
I have to study more about this subject. However I thought when we have a same vertex with two different couplings we can use re-parameterisation and change these two parameters to one . for instance when we have "Z.f Z.f ~H3 ~H3" vertex with la3 and la2 couplings we can remove these two terms from the potential and add just one term with coupling (la=la2+la3).

sincerely

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MohammadMohammadidoust (m23mohamadidoust) said :
#9

Thanks Alexander Belyaev, that solved my question.