Speaker
Description
Deep-inelastic scattering at small Bjorken-$x$ is best studied in the dipole model, where the virtual photon emitted by the lepton projectile fluctuates into a quark--antiquark pair that propagates through the dense hadronic target. In this framework, the cross section is given as a convolution of an impact factor and target matrix elements of Wilson lines along nearly lightlike trajectories. The kinematic reach of the Electron--Ion Collider requires a formulation of the shock-wave formalism up to sub-eikonal accuracy. Moreover, the eikonal formulation of the dipole model is spin-blind. Consequently, helicity-dependent observables---most notably the polarized structure function
$g_1(x, Q^2)$---require a systematic inclusion of sub-eikonal interactions. Despite the efforts over the last few years from various collaborations, a complete understanding of the effect of sub-eikonal corrections on the DIS cross section has not yet been settled.
In this talk, I will present a momentum-space formulation of high-energy DIS beyond the eikonal approximation. The formalism is suitable for the phenomenology of future polarized and unpolarized measurements at the Electron--Ion Collider. Building on quark and gluon propagators in a shock-wave background computed to sub-eikonal accuracy in my previous work, I derive the corresponding momentum-space Feynman rules and compute the sub-eikonal corrections to the DIS cross section for polarized and unpolarized structure functions. To this end, I isolate the operator structures that generate helicity sensitivity at small-$x$ and provide a direct bridge between the sub-eikonal high-energy OPE and momentum-space DIS for polarized and unpolarized structure functions.
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