I have a toy UFO model and I want to write a completely new propagator for a massive gluon that contains mathematical functions such as hyperbolic tangents in the denominator

The likely issue here is that the function atanh
will not be defined in fortran.
So you will need to add the definition of such function.

I guess in this case the easiest
is to define it in the file
Fortran/functions.f
(you can also define it in function_library.py)

Cheers,

Olivier
> On 15 Jun 2020, at 18:05, Mikel <email address hidden> wrote:
>
> New question #691328 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/691328
>
> I have a toy UFO model that contains an extra particle: a massive gluon. I tried modifying the propagators.py file writing my propagator. It's a really long propagator, so here is an easier example:
>
> V3 = Propagator(name = "V3",
> numerator = "complex(0,1) * (-1 * Metric(l1, l2) + Metric(l1,'mu')* P('mu', id) * P(l2, id) / Mass(id)**2"
>
> denominator = " P('mu', id) * P('mu', id)- Mass(id)*Mass(id) + P('mu', id)*P('mu', id)/(144*pi)* (atanh(Sqrt(Mass(id)**2).real - atanh(Sqrt(P('mu', id) * P('mu', id))).imag)"
> )
>
> Can I write this types of propagators in propagators.py or should I write them in another module?
>
> Thanks,
> Mikel
>
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Dear Olivier,

Thanks for the answer. I found another bug. I started building my propagator step by step:

V3 = Propagator(name = "V3",
                numerator = "complex(0,1) * (Gamma('mu', 1, 2) * P('mu'), id + Mass(id) * Identity(1, 2))”,
                denominator = "P('mu', id) * P('mu', id) - Mass(id) * Mass(id) + complex(0,1) * P('mu', id)*P('mu', id)/(144*3.1416)”
  )

When running madgraph, I get the following bug message:

 Command "launch" interrupted with error:
  AttributeError : 'ALOHAExpressionParser' object has no attribute ‘f'

However, if I run it using the following propagator (the default one) mg5_aMC runs fine
  denominator = "P('mu', id) * P('mu', id) - Mass(id) * Mass(id) + complex(0,1) * Mass(id) * Width(id)”

Cheers,
Mikel

Hi,

I have tested with this:
V15 = Propagator(name = "V15",
  numerator = " -1 * Metric(1, 2) + (P(1,id)-Metric(1,'a')*P('a',id) ) * P(2,id)/Mass(id)**2 ",
  denominator = "P('mu', id) * P('mu', id) - Mass(id) * Mass(id) + complex(0,1) * P('mu', id)*P('mu', id)/(144*3.1416)"
        )

and it works nicely. Here is one of the helicity routine generated for that modified propagator
C This File is Automatically generated by ALOHA
C The process calculated in this file is:
C Gamma(3,2,-1)*ProjM(-1,1)
C
      SUBROUTINE FFV2PV15_3(F1, F2, COUP, M3, W3,V3)
      IMPLICIT NONE
      COMPLEX*16 CI
      PARAMETER (CI=(0D0,1D0))
      COMPLEX*16 TMP2
      COMPLEX*16 V3(6)
      COMPLEX*16 TMP1
      REAL*8 W3
      REAL*8 P3(0:3)
      REAL*8 M3
      COMPLEX*16 F1(*)
      COMPLEX*16 F2(*)
      COMPLEX*16 DENOM
      COMPLEX*16 COUP
      V3(1) = +F1(1)+F2(1)
      V3(2) = +F1(2)+F2(2)
      P3(0) = -DBLE(V3(1))
      P3(1) = -DBLE(V3(2))
      P3(2) = -DIMAG(V3(2))
      P3(3) = -DIMAG(V3(1))
      TMP1 = (P3(0)*P3(0)-P3(1)*P3(1)-P3(2)*P3(2)-P3(3)*P3(3))
      TMP2 = (F1(3)*(F2(5)*(P3(0)+P3(3))+F2(6)*(P3(1)+CI*(P3(2))))
     $ +F1(4)*(F2(5)*(P3(1)-CI*(P3(2)))+F2(6)*(P3(0)-P3(3))))
      FCT0 = 1D0/(M3*M3)
      DENOM = COUP/((-M3*M3+(1D0 + 0.00221048015166D0*CI)*(TMP1)))
      V3(3)= DENOM*(-1D0)*(+CI*(F1(3)*F2(5)+F1(4)*F2(6)))
      V3(4)= DENOM*(+CI*(F1(3)*F2(6)+F1(4)*F2(5)))
      V3(5)= DENOM*(F1(4)*F2(5)-F1(3)*F2(6))
      V3(6)= DENOM*(-CI*(F1(4)*F2(6))+CI*(F1(3)*F2(5)))
      END

Cheers,

Olivier