One of the chief limitations of viscous hydrodynamical models are that they make an
implicit assumption that the system under consideration is close to being thermal and
isotropic in momentum space. However, there are many situations in which this may not be
the case. In particular, this assumption fails in ultrarelativistic heavy ion collisions
at early times due to the rapid longitudinal expansion of the system. It also fails near
the "cold" edges of the interaction region where the system is better approximated by a
free streaming gas. I will present a new method to derive hydro-like dynamical equations
which does not rely on the assumption that the system is close to being isotropic in
momentum space. The resulting partial differential equations can equally well describe the
ideal hydrodynamical limit, the free streaming limit, and anything in between. In
addition, they can be shown to reduce to the 2nd order viscous hydrodynamical equations in
the limit that the system is close to being isotropic in momentum space.
Finally, I will present results of the numerical solution of these equations in order to
quantitatively describe the collective flow of matter created in heavy ion collisions.
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