Lattice Computations of Small-x Parton Distributions in a Model of Parton Densities in Very Large Nuclei

Abstract

Using weak coupling methods McLerran and Venugopalan~\cite{LV1} expressed the parton distributions in large nuclei as correlation functions of a two dimensional Euclidean field theory. The theory has the dimensionful coupling $g^2 \mu $, where $\mu^2\sim A^{1/3}$ is the valence quark color charge squared per unit area. We use a lattice regularization to investigate these correlation functions both analytically and numerically for the simplified case of $SU(2)$ gauge theory. In weak coupling ($g^2\mu L<< 5$), where $L$ is the transverse size of the nucleus, the numerical results agree with the {\it analytic} lattice weak coupling results. For $g^2\mu L>> 5$, no solutions exist at O($a^4$) where $a$ is the lattice spacing. This suggests an ill-defined infrared behavior for the two dimensional theory. A recent proposal of McLerran et al.~\cite{Kovner} for an {\it analytic} solution of the classical problem is discussed briefly.