Transasymptotics and hydrodynamization of the Fokker-Planck equation for gluons

TL;DR

This paper explores the complex non-linear transport and hydrodynamization of gluons in an expanding system, revealing non-perturbative effects, renormalized transport coefficients, and transient non-Newtonian behavior through advanced asymptotic and resurgent analysis.

Contribution

It introduces a novel transseries resummation scheme for the moments of the distribution function, extending the definition of transport coefficients into non-equilibrium regimes.

Findings

Transport coefficients are renormalized by non-hydrodynamic modes.

The UV series has a finite radius of convergence growing with shear viscosity.

The plasma exhibits transient non-Newtonian behavior during hydrodynamization.

Abstract

We investigate the non-linear transport processes and hydrodynamization of a system of gluons undergoing longitudinal boost-invariant expansion. The dynamics is described within the framework of the Boltzmann equation in the small-angle approximation. The kinetic equations for a suitable set of moments of the one-particle distribution function are derived. By investigating the stability and asymptotic resurgent properties of this dynamical system, we demonstrate, that its solutions exhibit a rather different behavior for large (UV) and small (IR) effective Knudsen numbers. Close to the forward attractor in the IR regime the constitutive relations of each moment can be written as a multiparameter transseries. This resummation scheme allows us to extend the definition of a transport coefficient to the non-equilibrium regime naturally. Each transport coefficient is renormalized by the non-perturbative contributions of the non-hydrodynamic modes. The Knudsen number dependence of the transport coefficient is governed by the corresponding renormalization group flow equation. An interesting feature of the Yang-Mills plasma in this regime is that it exhibits transient non-Newtonian behavior while hydrodynamizing. In the UV regime the solution for the moments can be written as a power-law asymptotic series with a finite radius of convergence. We show that radius of convergence of the UV perturbative expansion grows linearly as a function of the shear viscosity to entropy density ratio. Finally, we compare the universal properties in the pullback and forward attracting regions to other kinetic models including the relaxation time approximation and the effective kinetic Arnold-Moore-Yaffe (AMY) theory.