Speaker
Description
Generalized transverse-momentum dependent distributions (GTMDs) provide the most differential two-parton correlators for hadronic phase-space tomography, while GPDs and TMDs arise as limiting or projected descriptions relevant to exclusive, diffractive, and transverse-momentum-sensitive measurements in the EIC era. I will describe a fixed-conformal-spin holographic framework in which this hierarchy is realized geometrically through string exchange in confining AdS backgrounds. The starting point is the fixed-spin channel of the GPD problem: conformal moments diagonalize the exchanged spin, make polynomiality in skewness manifest, and represent the all-skewness nucleon GPDs through spin-dependent form factors generated by t-channel string exchange. This construction is further constrained by a fixed-scale matching of holographic current-current correlators to QCD, where the ultraviolet photon/current vertex reproduces the conformal-OPE Wilson-coefficient structure at a single matching scale, while the infrared sensitivity is isolated in hadronic conformal moments. The new ingredient is the extension to gluon GTMDs at finite transverse separation b⊥. The gauge-invariant bilocal gluon operator, including its staple-shaped Wilson line, is represented by a classical string worldsheet attached to the same fixed-spin exchange that controls the GPD conformal moments. At leading order in the large-Nc and large-coupling semiclassical expansion, this gives a factorized description: a universal worldsheet soft factor encodes the strong coupling analogue of Collins–Soper rapidity evolution, while a stripped bulk exchange amplitude carries the hadronic dependence on skewness, momentum transfer, and confinement. The resulting impact-parameter representation connects the ultraviolet endpoint to the boundary GPD conformal moment and gives controlled predictions for nonperturbative transverse structure, including an algebraic soft-wall tail and, in a mixed hard-wall infrared limit with a massive transfer, a confining exponential falloff at large b⊥. Analytic continuation in conformal spin then reorganizes the same fixed-spin amplitudes into the low-x Regge regime, in direct analogy with the BPST Pomeron, without adding new non-perturbative input. In this sense, the phrase “strings attached” is literal: the GTMD is obtained by attaching the Wilson-line worldsheet to the fixed-spin string exchange that already controls the GPD sector.