Lightcone Expansion Beyond Leading Power

Abstract

We discuss recent developments in descriptions of processes using power expansion around the lightcone within Soft-Collinear Effective Theory. First, we present an overview of the systematically improvable framework that enables factorization of high-energy scattering processes beyond leading power in the expansion in ratios of energy scales. As an illustration of the relevant concepts, we describe the recently derived factorization theorem for the off-diagonal channel of the Drell-Yan production process at threshold. This example exposes endpoint divergences appearing in convolution integrals in factorization formulas. Lastly, we discuss the solution to these complications developed in the context of ''gluon thrust'' in $e^+e^-$ collisions.