FeynCalc 10.2.1: FCMultiLoopTID

[hyejungs-k]

Dear FeynCalc team,

We have identified some issues with "FCMultiLoopTID".
Some expressions that can be computed using FeynCalc 10.0.2 cannot be processed using FeynCalc 10.2.1.
The following expression is an example:
input =
MB2Spinor[Momentum[pout, D], MM, 1] . DiracGamma[Momentum[l1, D], D] . Spinor[Momentum[pin, D], MM, 1]
FeynAmpDenominator[PropagatorDenominator[Momentum[l1, D], MM], PropagatorDenominator[Momentum[l2, D], MB],
PropagatorDenominator[Momentum[l3, D], 0], PropagatorDenominator[Momentum[l2 - l3, D], MB],
PropagatorDenominator[Momentum[l1 + q, D], MM], PropagatorDenominator[Momentum[l1 - pout + q, D], 0],
PropagatorDenominator[0, Mh], PropagatorDenominator[Momentum[l2, D], MB],
PropagatorDenominator[Momentum[l2 - l3, D], MB]]

FCMultiLoopTID[input,{l1,l2,l3}] produces results in Mathematica 14.0.0 with FeynCalc 10.0.2, whereas the following errors are obtained in Mathematica 13.0.1,14.3, 15.0 with FeynCalc 10.2.1:

Error! Contract has encountered a fatal problem and must abort the computation. The problem reads: Something went wrong during prepareProductContractions.

Could there be a bug in FeynCalc 10.2.1? Could you also tell me where I can find the older versions of FeynCalc?
Unfortunately, I could not find them on the website.
I appreciate your help and answer already.

Kind regards,

Hyejung Stoeckinger-Kim

[vsht]

Hi,

I'm afraid that I cannot reproduce this bug. This is what I get when running your code:

Cheers,
Vlad

[hyejungs-k]

Hi,
Thanks for your quick reply! I reinstalled FeynCalc, and now I can reproduce your result. The difference is that this time I used 'automatic installation' instead of 'manual installation'.

However, 'automatic installation' does work in Mathematica 14.3 but not in Mathematica 15.0. My OS is ubuntu 26.04.
The following error message appears when attempting to install in Mathematica 15.0:

In[1]:= Import[
"https://raw.githubusercontent.com/FeynCalc/feyncalc/master/install.m"]

During evaluation of In[1]:= Import::nfurl: Unable to retrieve data from https://raw.githubusercontent.com/FeynCalc/feyncalc/master/install.m. Consult Internal`$LastInternalFailure for potential information.

Out[1]= $Failed

I can now use FeynCalc in both Mathematica 14 and 15, but I cannot understand why 'automatic installation' does not work in Mathematica 15.

Best regards,

Hyejung

[vsht]

Hi,

it looks like it cannot connect to GitHub for some reason, but in my case automatic installation on Mathematica 15.0 works without any issues.

Cheers,
Vlad

[vsht]

By the way, if you're doing calculations beyond 1-loop, I would not recommend using FCMultiLoopTID at all. The new formalism with GLI and FCTopology introduced in version 10 is much better suited for multiloop projects.