Hydrodynamic attractors for Gubser flow.

The Boltzmann equation is solved in the relaxation time approximation using a hierarchy of angular moments of the distribution function. Our solution is obtained for an azimuthally symmetric radially expanding boost-invariant conformal system that is undergoing Gubser flow. The solution of moments that we get after truncating the infinite set of equations at various orders is compared to the exact kinetic solution. The dynamics of transition from an early time collisionless free streaming to the hydrodynamic regime at late times is described by the presence of fixed points. The attractor solution is found for various orders of moments as an interpolation between these fixed points. For arbitrary initial conditions, it is found that the solution approaches the attractor when the non-hydrodynamic modes decay. The relation of moments to various approximations of relativistic viscous hydrodynamics is investigated.