Interpretation of the outputs

[huansouza]

Hi,

I'm using FeynCalc with TARCER and when I use the function TarcerExpand, the outputs are a bit strange to me,

In the first case, I used the external momentum outside the TarcerExpand function and I obtained a clean result. In the second case, I used the external momentum inside the TarcerExpand function and the result is very different. Besides that, there are some expressions that I never saw before, like Momentum^{(1,0)} (p,4).

My question is, what is the correct form of use this function and if it is the second one, what does mean these expressions like Momentum^{(1,0)} (p,4)?

Cheers,

Huan.

[vsht]

As you can see, TarcerExpand is not designed to expand amplitudes, only integrals. When you give it an amplitude, it
tries to apply Series to all occurrences of D, which creates such weird output:

Series[FCI@SPD[a, b] /. D -> 4 - 2 ep, {ep, 0, 2}]

The correct way would be to apply TarcerExpand only to integrals. Just use FCLoopExtract as explained in
arXiv:1601.01167.

[huansouza]

I didn't know about that, it worked properly. Thank you again!