Reduction of one-loop tensor form factors to scalar integrals: a general scheme Original Research Article

A general method for reducing tensor form factors, which appear in one-loop calculations in dimensional regularization, to scalar integrals is presented. The method is an extension of the reduction scheme introduced by Passarino and Veltman [Nucl. Phys. B 160 (1979) 151] and is applicable in all regions of parameter space including those where the kinematic Gram determinant vanishes. New relations between the form factors that are valid for the vanishing Gram determinant play a key rôle in the extended scheme.