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Jun 15, 2020 at 08:38 AM

IR singularities with squared amplitudes produced by MadLoop

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Hello,

I’m trying to use MadLoop to generate a standalone library for some processes with EW loop corrections, and have a few questions:
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, 

Xiang Lv