Amputate does not preserve D-4 dimension of DiracGamma[Momentum[q, D - 4], D]

[ZhiteYu]

Hi,

I think I found a bug in Amputate related to evanescent (D-4)-dimensional momenta.

Minimal example is given below. After amputation, the result behaves as if the amputated object were D-dimensional. Expected behavior: Amputate should preserve the evanescent dimension information, i.e. a factor originating from DiracGamma[Momentum[q, D - 4], D] should remain associated with (D - 4) rather than being turned into a D-dimensional object.

DiracGamma[Momentum[q, D - 4], D]
% // Amputate[#, q] & //
  FCCanonicalizeDummyIndices[#, 
    LorentzIndexNames -> {\[Rho], \[Sigma], \[Gamma], \[Delta]}] & //
  Calc

[vsht]

Amputate is not part of the "regular" FeynCalc toolset anymore:

https://github.com/orgs/FeynCalc/discussions/356

Everything in the FeynCalcLegacy add-on is kind of frozen, i.e. the stuff is there for people who might need it, but
it will not be maintained anymore.

I agree that it would be good to have a proper replacement for Amputate that can truncate different external states, but I don't really have time for that at the moment.