Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions

TL;DR

This paper analytically studies the early evolution of gluon fields in high-energy nuclear collisions, revealing hydrodynamic-like energy flow and angular momentum generation from initial conditions.

Contribution

It provides the first analytic recursive solutions to Yang-Mills equations describing initial gluon field dynamics at very high energies.

Findings

Analytic expressions for initial chromo-electric and chromo-magnetic fields.

Identification of hydrodynamic-like transverse energy flow.

Discovery of rapidity-odd energy flow generating angular momentum.

Abstract

Nuclei colliding at very high energy create a strong, quasi-classical gluon field during the initial phase of their interaction. We present an analytic calculation of the initial space-time evolution of this field in the limit of very high energies using a formal recursive solution of the Yang-Mills equations. We provide analytic expressions for the initial chromo-electric and chromo-magnetic fields and for their energy-momentum tensor. In particular, we discuss event-averaged results for energy density and energy flow as well as for longitudinal and transverse pressure of this system. Our results are generally applicable if $\tau < 1/Q_s$. The transverse energy flow of the gluon field exhibits hydrodynamic-like contributions that follow transverse gradients of the energy density. In addition, a rapidity-odd energy flow also emerges from the non-abelian analog of Gauss' Law and generates non-vanishing angular momentum of the field. We will discuss the space-time picture that emerges from our analysis and its implications for observables in heavy ion collisions.