Collins-Soper Kernel from the QCD Instanton Vacuum
A framework for evaluating the nonperturbative soft functions of TMD factorization in the QCD instanton vacuum, from which the Collins-Soper kernel governing the rapidity evolution of transverse-momentum-dependent parton distributions is derived. Combined with the perturbative contribution it matches lattice and phenomenological results, depends only logarithmically on the large quark transverse separation (constraining its parametrization), and is formulated in Euclidean signature so lattice calculations compare directly via analytic continuation.
Collins-Soper Kernel in the QCD Instanton Vacuum
Transverse-momentum-dependent parton distributions (TMDs) describe how quarks and gluons are distributed in both longitudinal momentum and transverse position inside a fast-moving hadron, and they un…