Spin Dependent Structure Function $g_1$ at Low $x$

TL;DR

This paper reviews theoretical models predicting the behavior of the spin-dependent structure function g_1 at low x, emphasizing the significance of double logarithmic effects and providing predictions relevant for HERA experiments.

Contribution

It presents a unified scheme combining Altarelli-Parisi evolution with double ln^2(1/x) resummation for g_1 at low x, including predictions for polarized gluon distributions.

Findings

Double ln^2(1/x) effects are significant at low x.

Predictions indicate observable effects at HERA.

Provides polarized gluon distribution estimates at low x.

Abstract

Theoretical expectations concerning small $x$ behaviour of the spin dependent structure function $g_1$ are summarised. This includes discussion of the Regge pole model predictions and of the double $ln^2(1/x)$ effects implied by perturbative QCD. The quantitative implementation of the latter is described within the unified scheme incorporating both Altarelli-Parisi evolution and the double $ln^2(1/x)$ resummation. The double $ln^2(1/x)$ effects are found to be important in the region of $x$ which can possibly be probed at HERA. Predictions for the polarized gluon distribution $\Delta G(x,Q^2)$ at low $x$ are also given.