Numerical Approach to Calculation of Feynman Loop Integrals
  In this paper, we describe a numerical approach to evaluate Feynman loop integrals. In this approach the key technique is a combination of a numerical integration method and a numerical extrapolation method. Since the computation is carried out in a fully numerical way, our approach is applicable to one-, two- and multi-loop diagrams. Without any analytic treatment it can compute diagrams with not only real masses but also complex masses for the internal particles. As concrete examples we present numerical results of a scalar one-loop box integral with complex masses and two-loop planar and non-planar box integrals with masses. We discuss the quality of our numerical computation by comparisons with other methods and also propose a self consistency check. 
F.Yuasa, T.Ishikawa, Y.Kurihara, J.Fujimoto, Y.Shimizu, N.Hamaguchi,   E.de Doncker and K.Kato
hep-ph