Anomalous diffusion in QCD matter

TL;DR

This paper investigates how quantum effects influence the transverse momentum broadening of fast partons in dense QCD matter, revealing a universal, super-diffusive distribution with anomalous scaling properties.

Contribution

It introduces a leading logarithmic analysis showing universal scaling behavior and super-diffusive properties in transverse momentum broadening in QCD matter.

Findings

Distribution depends on a single scaling variable $k^2_ot/Q^2_s$

The typical transverse momentum scale grows logarithmically with system size

The distribution exhibits a heavy tail indicating super-diffusive Lévy flight behavior

Abstract

We study the effects of quantum corrections on transverse momentum broadening of a fast parton passing through dense QCD matter. We show that, at leading logarithmic accuracy the broadening distribution tends at late times or equivalently for large system sizes $L$ to a universal distribution that only depends on a single scaling variable $k^2_\perp/Q^2_s$ where the typical transverse momentum scale increases with time as $\ln Q_s^2 \simeq (1+2 \beta ) \ln L - \frac{3}{2}(1+\beta )\,\ln\ln L$ up to non-universal terms, with an anomalous dimension $\beta \sim \sqrt{\alpha_s} $. This property is analogous to geometric scaling of gluon distributions in the saturation regime and traveling waves solutions to reaction-diffusion processes. We note that since $\beta >0$ the process is super-diffusive, which is also reflected at large transverse momentum where the scaling distribution exhibits a heavy tail $k_\perp^{4-2\beta }$ akin to L\'{e}vy random walks.