Perturbation theory in (2,2) signature

Understand

We identify a natural analytic continuation in four dimensions from Minkowski signature to a signature with two time-like momentum components.

• For two, three and four-point diagrams at fixed external momenta, this continuation can be implemented as a countour 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.