Polarized Dipole Scattering Amplitudes meet the Valence Quark Model

The recently revised small-x helicity evolution, resumming the double-logarithmic factor, ₛ² (1/x), allows for the study of helicity distributions of quarks and gluons at small Bjorken x, corresponding to high center-of-mass energy. In this work, we calculate the moderate-x initial conditions in the regime, ₛ ² (1/x) 1, for the small-x helicity evolution using a light-front valence quark model of the proton, which provides additional physical information about the target. The perturbative emission and absorption of a gluon by the valence quarks are also included. The results, given in Eqs. (35), provide a new set of initial conditions with a significantly reduced number of free parameters than conventional models. Consequently, the predictive power of small-x helicity evolution is expected to improve once the initial conditions from this work are incorporated.