Azimuthal Anisotropies at High Momentum from Purely Non-Hydrodynamic Transport

TL;DR

This paper introduces a new non-hydrodynamic expansion method for kinetic theory applicable at large mean free paths, successfully calculating high-momentum azimuthal anisotropies in heavy-ion collisions.

Contribution

It develops a systematically improvable eremitic expansion in the large mean free path limit, extending kinetic theory beyond hydrodynamics for high-gradient regimes.

Findings

Calculated azimuthal anisotropies at high transverse momentum in Pb+Pb and p+Pb collisions.

Demonstrated the eremitic expansion's validity where hydrodynamics fails.

Provided a new approach for non-hydrodynamic transport analysis.

Abstract

In the limit of short mean free path, relativistic kinetic theory gives rise to hydrodynamics through a systematically improvable gradient expansion. In the present work, a systematically improvable expansion in the opposite limit of large mean free path is considered, describing the dynamics of particles which are almost, but not quite, non-interacting. This non-hydrodynamic "eremitic" expansion does not break down for large gradients, and may be useful in situations where a hydrodynamic treatment is not applicable. As applications, azimuthal anisotropies at high transverse momentum in Pb+Pb and p+Pb collisions at $\sqrt{s}=5.02$ TeV are calculated from the first order eremitic expansion of kinetic theory in the relaxation time approximation.