A method for computing Feynman amplitudes with branch cuts

摘要

By several simple examples, we demonstrate a method of expanding Feynman amplitudes about a point in the upper half s-plane, and re-summing by the Padé method. This technique moves the branch cuts into the lower half-plane, and allows direct computation of amplitudes in the physical region. For more complicated amplitudes, it may be preferable to use two-variable approximants for re-summing.