Infrared singularities and the high-energy limit

Abstract

We review recent results on the high-energy limit of gauge amplitudes, which can be derived from the universal properties of their infrared singularities. Using the dipole formula, a compact ansatz for infrared singularities of massless gauge amplitudes, and taking the high-energy limit, we provide a simple expression for the soft factor of a generic high-energy amplitude, valid to leading power in $t/s$ and to all logarithmic orders. This gives a direct and general proof of leading-logarithmic Reggeization for infrared divergent contributions to the amplitude, and it shows how Reggeization breaks down at NNLL level. We further show how the dipole formula constrains the high-energy limit of multi-particle amplitudes in multi-Regge kinematics, and how, on the other hand, Regge theory constrains possible corrections to the dipole formula.