Unveiling the Collins-Soper kernel in inclusive DIS at threshold

TL;DR

This paper revisits the factorization in inclusive deep inelastic scattering near threshold, clarifies soft radiation effects, and introduces a lattice method to compute the Collins-Soper kernel, advancing understanding of rapidity evolution.

Contribution

It provides a detailed analysis of off-lightcone effects in DIS near threshold and proposes a novel lattice approach to calculate the Collins-Soper kernel.

Findings

Clarified the role of soft radiation and rapidity divergences.

Established a universal Collins-Soper kernel in the context of inclusive DIS.

Proposed a new lattice method for computing the kernel.

Abstract

We revisit the factorization of inclusive deep inelastic scattering near the kinematic threshold to explicitly track off-lightcone effects. Particle production develops around two opposite near-lightcone directions like in transverse-momentum-dependent processes, and the Collins-Soper kernel emerges as a universal function in the rapidity evolution of the relevant parton correlators. We clarify outstanding issues regarding soft radiation and rapidity divergences, and uncover a new way to calculate the Collins-Soper kernel on the lattice with collinear operators.