Small-x Evolution of the Gluon Generalized Parton Distribution Eg of the Nucleon

TL;DR

This paper investigates the small-$x$ evolution of the gluon GPD $E_g$ in the nucleon, revealing Regge behavior and saturation effects, which are crucial for understanding nucleon spin structure at high energies.

Contribution

It presents the first analysis of the small-$x$ evolution of $E_g$, showing Regge behavior and saturation effects, impacting nucleon spin sum rule modeling.

Findings

$E_g$ exhibits Regge behavior similar to the BFKL Pomeron.

$E_g$ saturates similarly to $H_g$ at small-$x$.

Results influence nucleon spin sum rule calculations.

Abstract

We study the small-$x$ evolution equation for the gluon generalized parton distribution (GPD) $E_g$ of the nucleon. It is shown that $E_g$ at vanishing skewness exhibits the Regge behavior identical to the BFKL Pomeron, despite its association with nucleon helicity-flip processes. We also consider the effect of gluon saturation and demonstrate that $E_g$ gets saturated in the same way as its helicity-nonflip counterpart $H_g$. Our result has a direct impact on the modeling of $E_g$ as well as the small-$x$ contribution to nucleon spin sum rules.