Name: Vladyslav Shtabovenko (email_not_shown)
Date: 11/27/16-08:26:29 PM Z


Dear Jong-Wan,

the result

I \[Pi]^2 (-((A0[m^2] GA[\[Alpha]])/(2 (1 - D))) +
    2 FV[p, \[Alpha]] GS[p] - ((2 - 4 D + D^2) A0[m^2] FV[
      p, \[Alpha]] GS[p])/(2 (1 - D) m^2))

is correct. What is (in general) not correct and dangerous, is to do

exp /. D->4

Please have a look at

https://github.com/FeynCalc/feyncalc/wiki/FAQ#limitto4

this should explain it better.

Cheers,
Vladyslav

Am 24.11.2016 um 06:17 schrieb Jong-Wan Lee:
> Dear Frederik,
>
> I used to use Feyncalc 8.2.0 on Mathematica 9, and recently I started to
> use Feyncalc 9.2.0 on Mathematica 11. However, I encountered a problem
> in doing the one loop integral,
>
> SP[p,p]=m^2;(*kinematics*)
> SetOptions[B0, BReduce->True, B0Unique->True, B0Real->True];
> OneLoop[k, FVD[k, \[Alpha]].GSD[k] FAD[{k, m}, p - k]];
>
> In the old version, I have
>
> I \[Pi]^2 (m^2 DiracGamma[LorentzIndex[\[Alpha]]]+8
> DiracGamma[Momentum[p]] Pair[LorentzIndex[\[Alpha]],
> Momentum[p]] )/9 + (
> I \[Pi]^2 A0[m^2] (m^2 DiracGamma[LorentzIndex[\[Alpha]]] +
> 2 DiracGamma[Momentum[p]] Pair[LorentzIndex[\[Alpha]],
> Momentum[p]]))/(6 m^2)
>
> but, in the new version, I have
>
> 2 I \[Pi]^2 DiracGamma[Momentum[p]] Pair[LorentzIndex[\[Alpha]],
> Momentum[p]] + (
> I \[Pi]^2 A0[m^2] (m^2 DiracGamma[LorentzIndex[\[Alpha]]] +
> 2 DiracGamma[Momentum[p]] Pair[LorentzIndex[\[Alpha]],
> Momentum[p]]))/(6 m^2)
>
> Comparing the two results, I find that the second terms which include
> the UV divergence terms are same, but the first finite terms are
> different. In fact the result from the old version is the correct one.
> Can you help me to resolve this problem?
>
> Best regards,
> Jong-Wan




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