Polarized Dipole Scattering Amplitudes meet the Valence Quark Model

TL;DR

This paper develops a new set of initial conditions for small-$x$ helicity evolution in protons, using a valence quark model to improve predictions of quark and gluon helicity distributions at high energies.

Contribution

It introduces a valence quark model-based approach to determine initial conditions for small-$x$ helicity evolution, reducing free parameters and enhancing predictive accuracy.

Findings

Provides explicit initial conditions equations (Eq. 35) for helicity evolution.

Reduces the number of free parameters compared to traditional models.

Enhances the predictive power of small-$x$ helicity evolution studies.

Abstract

The recently revised small-$x$ helicity evolution, resumming the double-logarithmic factor, $\alpha_s\ln^2(1/x)$, 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, $\alpha_s \ln^2(1/x)\sim 1$, 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.