Hydrodynamic attractor of a hybrid viscous fluid in Bjorken flow

TL;DR

This paper investigates the nonequilibrium evolution of a hybrid viscous fluid in Bjorken flow, revealing a hydrodynamic attractor that explains different thermalization behaviors in heavy-ion collisions.

Contribution

It introduces a hydrodynamic attractor framework for a hybrid viscous fluid with two interacting components, capturing early-time dynamics and varying hydrodynamization times.

Findings

Identification of a hydrodynamic attractor in hybrid viscous fluids.

Different hydrodynamization times for the two sectors.

Total system acts like a single viscous fluid with effective shear viscosity.

Abstract

The nonequilibrium evolution in a boost-invariant Bjorken flow of a hybrid viscous fluid model containing two interacting components with different viscosities, such that they represent strongly and weakly self-coupled sectors, is shown to be characterized by a hydrodynamic attractor which has an early-time behavior that is reminiscent of the so-called bottom-up thermalization scenario in heavy-ion collisions. The hydrodynamization times for the two sectors can differ strongly, with details depending on the curve realized on the two-dimensional attractor surface, which might account for different scenarios for small and large systems in nuclear collisions. The total system behaves like a single viscous fluid with a dynamically determined effective shear viscosity.