UV singularities with amplitudes produced by MadLoop5

Hi,

When generating your line,
you will see the following print statement:
INFO: Contributing diagrams generated: 1 Born, 151(+6) loops, 18 R2, 14 UV

Cheers,

Olivier

> On 6 Dec 2021, at 05:15, Halley Xiong <email address hidden> wrote:
>
> New question #699766 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/699766
>
> Hi, experts
>
> I'm trying to generate a process with only EW corrections by MadLoop5, and with loop generated I choose one diagram that I'm interested with, which is a pentagon diagram. I input
>
> MG5_aMC> generate e- u > ve d h [virt=QED]
> MG5_aMC> output euloop
>
> MG5_aMC> launch -f
>
>> cd <MG_root>/euloop/SubProcesses/P0_emu_vedh
>> make check
>> ./check
>
> the output is
>
> ---------------------------------
> Stable kinematic configuration (SPS).
> Relative accuracy = 0.45E-12
> MadLoop return code = 213
> ---------------------------------
> ---------------------------------
> Matrix element born = 1.6127107055860164E-009 GeV^ -2
> Matrix element finite = -3.2234529459933569E-012 GeV^ -2
> Matrix element 1eps = 4.0870682586144573E-012 GeV^ -2
> Matrix element 2eps = -2.6543689873060851E-012 GeV^ -2
> ---------------------------------
> finite / (born*ao2pi) = -0.10642967284253363
> 1eps / (born*ao2pi) = 0.13494390795749397
> 2eps / (born*ao2pi) = -8.7640064134795692E-002
>
> As far as I know this diagram only have IR pole, I wonder whether the result of single pole include UV pole, or UV conterterms?
>
> Sincerely,
> Halley
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Thanks, this solved my problem!

Hello,

I’m trying to use MadLoop to generate a standalone library for some processes with EW loop corrections, and have a few questions: https://apkslover.com/
1. I’m confused by the IR poles in the results. For instance, for the simple QED process e- e+ -> mu- mu+, I did

define exc = g0 g+ g- h gha ghz ghwp ghwm z u c d e- b s mu- ta+ ta- w+
generate e- e+ > mu- mu+ QCD=0 [virt=QED] /exc

which produced a loop graph with a top quark loop on the photon propagator. When I did

launch -f

I got the result

|| Total(*) Born contribution (GeV^0):

| Born = 1.1012911820047121e-02

|| Total(*) virtual contribution normalized with born*alpha_S/(2*pi):

| Finite = -2.1842211753457780e-01

| Single pole = -1.1685343497245081e-01

| Double pole = 0.0000000000000000e+00

As far as I know, this loop graph should not have an IR singularity. Do you know the reason for the non-zero single pole?
2. Can I use the subtraction method in MadFKS to compute photon radiative corrections? It seems that only QCD NLO radiative corrections are available.
3. When I run MadLoop in standalone mode, how can I set a dynamical renormalization scale? The process I’m considering is again EW loop graphs. I don’t find the setscal.f file in my output.
Thanks,

I guess that when deal with one-loop diagrams, Madloop would generate counter-terms to cancel uv divergences, but there are not one-by-one correspondence between uv singular loop diagrams and counter-terms. So when you generate a process and exclude some diagrams you don't want, the uv divergences cannot be cancelled, so there appear non-zero pole.
2. I think MadFKS can deal with electroweak corrections, it's already been mentioned in the paper : arxiv: 1804.10017
3. when you generate a process and output your_file_name, there is 'your_file_name/Source/MODEL/couplings.f', in which has 'SUBROUTINE UPDATE_AS_PARAM2(MU_R2,AS2)', but I'm not sure what's the following step. I'll discuss with my co-worker next time.

I'm not an expert, but I notice you put the question under my old question. If you want a more professional answer, you can ask your question in a new box because I'm not sure whether your question will be noticed by experts in this old box.

Cheers

UV singularities, or ultraviolet singularities, are mathematical divergences that arise in quantum field theories when calculating physical quantities involving virtual particles. These singularities are a result of integrating over loop momenta that extend to arbitrarily high energies (short distances), which leads to infinite results when performing calculations naively.https://resultadosdeltris.net/

MadLoop5 is a program used for the automatic generation of one-loop amplitudes in particle physics processes. It's part of the MadGraph package, which is widely used for simulating and calculating high-energy physics processes.

When calculating loop amplitudes using tools like MadLoop5, one of the major challenges is dealing with these UV singularities. They need to be regularized and renormalized to obtain finite and physically meaningful results. Renormalization involves introducing counterterms into the theory to absorb the divergences, ensuring that observables are well-defined and finite.