Boost covariant gluon distributions in large nuclei

TL;DR

The paper develops a boost-covariant description of gluon distributions in large nuclei at small x by constructing a simple model for the color charge distribution in the fragmentation region. Building on analytical solutions of non-Abelian Weizsäcker–Williams fields, it derives χ(η,Q^2) and a corresponding gluon distribution that remains boost-invariant across rapidity when χ is specified. A parameter κ encodes the average color charge per nucleon per unit rapidity and, together with nucleon parton densities (via GRV fits), sets the initial conditions for small-x evolution via a Wilson renormalization-group framework that connects to DGLAP/BFKL-like dynamics. The work discusses implications for gluon shadowing in large nuclei, clarifies the regime of validity (classical, weak coupling) and outlines paths to include quantum corrections and phenomenological constraints.

Abstract

It has been shown recently that there exist analytical solutions of the Yang-Mills equations for non-Abelian Weizsäcker-Williams fields which describe the distribution of gluons in large nuclei at small x. These solutions however depend on the color charge distribution at large rapidities. We here construct a model of the color charge distribution of partons in the fragmentation region and use it to compute the boost covariant momentum distributions of wee gluons. The phenomenological applications of our results are discussed.