On attractor and fixed points in Bjorken flows

Understand

We consider a plasma of massless particles undergoing Bjorken expansion, mimicking the matter created in ultra-relativistic heavy ion collisions.

• We study the transition to hydrodynamics using kinetic theory in the relaxation time approximation.
• By allowing the relaxation time to depend on time, we can monitor the speed of the transition from the collisionless regime to hydrodynamics.
• By using a special set of moments of the momentum distribution, we reduce the kinetic equation to a coupled mode problem which encompasses all versions of second order viscous hydrodynamics for Bjorken flows.