Perturbation theory in (2,2) signature

We identify a natural analytic continuation in four dimensions from Minkowski signature to a signature with two timelike momentum components. For two-, three-, and four-point diagrams whose external momenta define a scattering plane, this continuation can be implemented as a contour deformation that leaves dependence on the momenta unchanged. For arbitrary ultraviolet-finite scalar diagrams it is possible to do two integrals per loop in terms of simple poles in the new signature. This results in a representation of any such diagram as a sum of terms, each with two remaining integrals per loop.