Name: V. Shtabovenko Date: 10/21/17-09:10:34 AM Z
In general, the best strategy for such complicated integrals is to
first
rewrite them in terms of the coefficient functions
amp = Pair[Momentum[k], Momentum[p1]]^3
FAD[{k, lam}, {(k - q),
lam}, {(k - p1), m}, {(k + p2), M}];
res = TID[amp, k, UsePaVeBasis -> True, ToPaVe -> True]
which quickly returns a rather compact result
-3 I \[Pi]^2 PaVe[0, 0,
1, {SPD[p1, p1], SPD[p1, p1] + 2 SPD[p1, p2]
Then, depending on what one wants to do, one can
1) Evaluate the coefficient functions numerically using LoopTools,
Collier or whatever other package
2) Evaluate the coefficient functions analytically via Package-X by
using PaXEvaluate from the FeynHelpers extension
3) Reduce the coefficient functions to scalar integral, which would
of
course generate a huge amount of terms, e.g.
res[[1]] // PaVeReduce
Cheers,
Vladyslav
> I’m trying to do an integral that FeynCalc chokes on. The message
returned
> is the usual
>
> FYI: Tensor integrals of rank higher than 3 encountered; Please use
the
> option CancelQP -> True or OneLoopSimplify->True or use another
program.
>
> However, it appears that CancelQP->True is the default, and
OneLoopSimplify
> expresses the results in terms of Contract3, which doesn’t seem to
exist.
>
> The integrals are box diagrams, and a typical term would look
something like
>
> (k.p1)^3 /
[k^2-lam^2][(k-q)^2-lam^2][(k-p1)^2-m^2][(k+p2)^2-M^2]
>
> where p1^2=m^2 and p2^2=M^2. This term looks innocent enough, and in
fact
> looks to me like it IS of rank 3. By a lot of fudging and
manipulating I
> managed to get a result using ScalarProductCancel, but it is hit and
miss
> for various terms in the amplitude.
>
> Is there a fix in FeynCalc, or do I have to use another program (and
if so,
> which one)?