The analytic continuation of the high-energy parton-parton scattering amplitude with an IR cutoff

Abstract

The high-energy parton-parton scattering amplitude can be described, in the c.m.s., by the expectation value of two infinite Wilson lines, running along the classical trajectories of the two colliding particles. The above description suffers from IR divergences (typical of 3 + 1 dimensional gauge theories), which can be regularized by considering finite Wilson lines, extending in proper time from -T to T (and eventually sending T to infinity). Generalizing the results of a previous paper, we give here the general proof that the expectation value of two IR-regularized Wilson lines, forming a certain hyperbolic angle in Minkowski space-time, and the expectation value of two IR-regularized Euclidean Wilson lines, forming a certain angle in Euclidean four-space, are connected by an analytic continuation in the angular variables and in the IR cutoff T. This result can be used to evaluate the IR-regularized high-energy scattering amplitude directly in the Euclidean theory.