Two-Loop Tensor Integrals in Quantum Field Theory
  A comprehensive study is performed of general massive, tensor, two-loop Feynman diagrams with two and three external legs. Reduction to generalized scalar functions is discussed. Integral representations, supporting the same class of smoothness algorithms already employed for the numerical evaluation of ordinary scalar functions, are introduced for each family of diagrams. 
S. Actis, A. Ferroglia, G. Passarino, M. Passera, S. Uccirati