Conventions for Levi Civita contraction
Hi again,
i am considering the process e+e - > t t~ / A and comparing the squared matrix element. FORM, FeynCalc and a calculation by hand give the same result and for a given phase space point i obtain
0.00418983, whereas MadGraph gives 0.00516665. I am able to reproduce the value from MadGraph if i change the signs in the terms generated by the gamma5 contributions coming from the vertices. So i get a relation of the form
eps_(\mu \sigma \nu \rho)*eps^(\mu \sigma \alpha \beta) = 2*g^(\alpha \rho)*g^(\beta \nu) - 2*g^(\alpha \nu)*g^(\beta \rho) with eps^(0123) = +1
which leads my result, but changing the overall sign on the right hand side gives the result from MadGraph. Therefore i am wondering what kind of conventions MadGraph is using which cause the difference.
Another question regarding the process e+ e- > t t ~ g / Z: the squared matrix elements are here the same, but i get a difference in the value for the cross section (my result 0.06272 pb, Madgraph 0.054 pb). I checked that i use the same values (especially no running for alphaS, no widths at all, same cuts (there is only one relevant cut for the gluon energy which i set to 20 GeV), cms energy 1 TeV). Do you have any idea what might cause this deviation?
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