Speaker
Description
We introduce a general framework based on topologically active configurations, known as instantons, in the QCD vacuum to evaluate the non-perturbative transverse partonic structure of hadrons. Specifically, we derive the transverse-momentum-dependent parton distribution functions (TMDPDFs) for the pion, kaon, and rho meson, along with the Collins-Soper (CS) kernel, which governs the rapidity evolution of TMDPDFs. Our results offer a tomographic view of the pion and kaon parton structure in both the parton fraction $x$ and transverse space $b$. The derived CS kernel, when supplemented with perturbative contributions, aligns well with recent lattice QCD results and phenomenological fits. Additionally, we find that the CS kernel exhibits a logarithmic dependence on large quark transverse separation $b$, providing a crucial constraint for its phenomenological parametrization. Lastly, our framework allows direct comparison with lattice calculations in Euclidean signature, offering a novel approach to evaluating the soft function and extracting the CS kernel via analytical continuation.
