Simplifying 5-point tensor reduction

The 5-point tensors have the property that after insertion of the metric tensor $g^{μν}$ in terms of external momenta, all $g^{μν}$-contributions in the tensor decomposition cancel. If furthermore the tensors are contracted with external momenta, the inverse 5-point Gram determinant $()_5$ cancels automatically. If the remaining 4-point sub-Gram determinant ${s\choose s}_5$ is not small then this approach appears to be particularly efficient in numerical calculations. We also indicate how to deal with small ${s\choose s}_5$. Explicit formulae for tensors of degree 2 and 3 are given for large and small (sub-) Gram determinants.

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