MadGraph5_aMC@NLO

Unable to generate cross sections for loop processes

Asked by Kuntal Pal

Hello Experts!

I am trying to run the following code in MadGraph5

import sm

generate h > a a [noborn=QED]
output madevent
launch

which returns a configuration error.

Error detected in "generate_events run_01"
write debug file /Users/kuntalpal/PROC_loop_qcd_qed_sm_28/run_01_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/mg5amcnlo
MadGraph5Error : A compilation Error occurs when trying to compile /Users/kuntalpal/PROC_loop_qcd_qed_sm_28/SubProcesses/PV0_0_1_h_aa.
 The compilation fails with the following output message:
     gfortran -w -fPIC -ffixed-line-length-132 -O3 -c polynomial.f -o polynomial.o -I /Users/kuntalpal/Downloads/MG5_aMC_v2_7_3/HEPTools/include -I /Users/kuntalpal/Downloads/MG5_aMC_v2_7_3/HEPTools/include
     gfortran -O -w -fbounds-check -fPIC -ffixed-line-length-132 -c check_sa.f -o check_sa.o -I /Users/kuntalpal/Downloads/MG5_aMC_v2_7_3/HEPTools/include -I /Users/kuntalpal/Downloads/MG5_aMC_v2_7_3/HEPTools/include
     check_sa.f:415:38:

       415 | CALL RAMBO(NEXTERNAL-2,ENERGY,PMASS(3),PRAMBO,WGT)
           | 1
     Error: Actual argument contains too few elements for dummy argument 'xm' (1/2) at (1)
     make: *** [check_sa.o] Error 1

 Please try to fix this compilations issue and retry.
 Help might be found at https://answers.launchpad.net/mg5amcnlo.
 If you think that this is a bug, you can report this at https://bugs.launchpad.net/mg5amcnlo

I would like to know what is causing this error.

Also not all loop processes return similar error.

For example

g g > W+ W- [QCD] works fine.

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

This seems that you are using an incompatible set of compiler and version of MG5aMC.
l would bet that you are using Gfortran 10? Is this correct ?

It is possible that the latest version of MG5aMC already fix that issue but I would not bet on that since I do not remember issue with that file before. So I will try to check.

Cheers,

Olivier

Revision history for this message
Kuntal Pal (kpal1995) said : 		#2

Yes the current version I have on my system is gfortran 10 and the Madgraph version is 2.7.3

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#3

Hi,

Here is a patch that fixes that specific issue:
https://bazaar.launchpad.net/~maddevelopers/mg5amcnlo/2.8.3.py2/revision/299
I personally think that GCC should not create an error in this particular case but ok I have implemented a work around.

I would advise to use the latest version with GCC10 since I would not be surprised that 2.8.2 has some additional fix for GCC10.

Cheers,

Olivier

Revision history for this message
Kuntal Pal (kpal1995) said : 		#4

Thank you very much ! The patch seems to work great so far. I had a separate question regarding loop processes. I can write something like

generate p p > t H j, H > b b~

for higgs decaying to b b~. What is the correct syntax for similar process but H > a a which is loop induced ?

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#5

We do not have such syntax for loop-induced decay.

The two work-around are
1) use the EFT approach for the Higgs decay
2) use MadSpin in the spinmode=none mode

Cheers,

Olivier

> On 11 Dec 2020, at 05:25, Kuntal Pal <email address hidden> wrote:
>
> Question #694424 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/694424
>
> Kuntal Pal posted a new comment:
> Thank you very much ! The patch seems to work great so far. I had a
> separate question regarding loop processes. I can write something like
>
> generate p p > t H j, H > b b~
>
> for higgs decaying to b b~. What is the correct syntax for similar
> process but H > a a which is loop induced ?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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