Hydrodynamization and Resummed Viscous Hydrodynamics

In this contributed chapter, I review our current understanding of theapplicability of hydrodynamics to modeling the quark-gluon plasma (QGP),focusing on the question of hydrodynamization/thermalization of the QGP and theanisotropic hydrodynamics (aHydro) far-from-equilibrium hydrodynamic framework.I discuss the existence of far-from-equilibrium hydrodynamic attractors andmethods for determining attractors within different hydrodynamical frameworks.I also discuss the determination of attractors from exact solutions to theBoltzmann equation in relaxation time approximation and effective kinetic fieldtheory applied to quantum chromodynamics. I then present comparisons of thekinetic attractors with the attractors obtained in standard second-viscoushydrodynamics frameworks and anisotropic hydrodynamics. I demonstrate that, dueto the resummation of terms to all orders in the inverse Reynolds number, theanisotropic hydrodynamics framework can describe both the weak- andstrong-interaction limits. I then review the phenomenological application ofanisotropic hydrodynamics to relativistic heavy-ion collisions using bothquasiparticle aHydro and second-order viscous aHydro. The phenomenologicalresults indicate that aHydro provides a controlled extension of dissipativerelativistic hydrodynamics to the early-time far-from-equilibrium stage ofheavy-ion collisions. This allows one to better describe the data and toextract the temperature dependence of transport coefficients at much highertemperatures than linearized second-order viscous hydrodynamics.