Speaker
Description
Generalized transverse-momentum-dependent distributions (GTMDs) provide a phase-space description of partons and a natural framework for studying orbital angular momentum in the nucleon. In particular, the canonical quark orbital angular momentum (OAM) density is encoded in a transverse-momentum moment of the GTMD $F_{14}$. Beyond tree level, however, this moment is ultraviolet divergent, and its relation to collinear distributions must be defined through a renormalized small-transverse-distance expansion, $b$.
In this talk, I will present our one-loop small-$b$ matching of $F_{14}$ onto collinear generalized parton distributions in the flavor-nonsinglet sector at zero skewness. A central feature is that, although $F_{14}$ belongs to the leading-twist GTMD parametrization, the OAM projection requires not only the twist-two GPDs $H$, $E$, and $\widetilde{H}$, but also the genuine twist-three quark–gluon–quark distributions $\Phi_F$ and $\widetilde{\Phi}_F$. I will outline the background-field calculation and the treatment of rapidity, ultraviolet, and collinear singularities, including soft-factor subtraction. I will also discuss how the resulting matching consistently connects CSS evolution of the finite-$b$ GTMD with DGLAP and BFLK evolution of the twist-two and twist-three collinear sectors. These results provide a perturbative bridge for interpreting proposed EIC observables sensitive to canonical quark OAM, by anchoring the short-distance GTMD to twist-two and genuine twist-three GPDs with consistent scale evolution.