Majorana Fermion with non-hermitian mediator

Asked by Vinicius on 2020-06-23

I implemented in Calchep a generic model that I am working. When I put in Calchep the process: S2 + N2 -> N1 + S1 (where S1,S2,N1 and N2 are majorana fermions, moreover this process is mediated by a non-hermitian boson U, that is neutral).
I do not understand why Calchep consider for this process (S2 + N2 -> N1 + S1 ), the contribution of theses two diagrams:

 S2 N1
=====@=====
              |
           U|
   N2 | S1
=====@=====
and
S2 N1
=====@=====
              |
\bar{U}|
 N2 | S1
=====@=====
Since theses contributions have the same vertices, same contribution, and equal amplitude.

Thanks,
Vinicius

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Alexander Belyaev (alexander.belyaev) said :
#1

Dear Vinicius,

since U is different from U*,
you can construct two diagrams with U going "up" and U going "down" if we look at the t-channel diagram.
So, CalcHEP works correctly, according to the model you have implemented.

Best,
Alexander

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Vinicius (viniciuslbo) said :
#2

Thanks a lot.

Best,
Vinicius

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Alexander Pukhov (pukhov) said :
#3

I guess your  Lagrangian contains  both {S2 N1 U } and {S2 N1 \bar{U}}
vertices. Thus you see 2 diagrams.

Best

    Alexander Pukhov

On 6/23/20 5:41 PM, Vinicius wrote:
> New question #691487 on CalcHEP:
> https://answers.launchpad.net/calchep/+question/691487
>
> I implemented in Calchep a generic model that I am working. When I put in Calchep the process: S2 + N2 -> N1 + S1 (where S1,S2,N1 and N2 are majorana fermion, moreover this process is mediated by a non-hermitian boson U, that is neutral).
> I do not understand why Calchep consider for this process (S2 + N2 -> N1 + S1 ), the contribution of theses two diagrams:
>
> S2 N1
> =====@=====
> |
> U|
> N2 | S1
> =====@=====
> and
> S2 N1
> =====@=====
> |
> \bar{U}|
> N2 | S1
> =====@=====
> Since theses contributions habe the same vertices, same contribution, and equal amplitude.
>
> Thanks,
> Vinicius
>