Authors:
H. Niemi (speaker), I. Bouras, G. S. Denicol, E. Molnar, Z. Xu, D. H. Rischke and C. Greiner

Title:
Transient fluid dynamics from kinetic theory: applications to heavy-ion collisions at LHC and RHIC

Abstract:

Relativistic fluid dynamics has become one of the main tools
in modelling the spacetime evolution of ultrarelativistic heavy-ion
collisions, and in extracting the properties like shear viscosity
of the strongly interacting matter. The system created in these
collisions is, however, small and short-lived, and thus it is not
clear that fluid dynamics can quantitatively describe the evolution.
Theoretically the applicability of fluid dynamics requires that the
Knudsen number, i.e. ratio of microscopic time or length scales
to macroscopic scales is small.

I will show estimates of the Knudsen numbers in the realistic
modelling of heavy-ion collisions [1], and estimate the maximum values
of shear viscosity to entropy ratio that we can use in fluid
dynamical description of the collisions. The recent estimates
of the shear viscosity of quark-gluon plasma are very close to
these maximum values, indicating that there can be large
corrections to the fluid dynamical behaviour.

Furthermore, I will shortly review how the transient fluid dynamics
emerges from the Boltzmann equation[2], and how the fluid dynamical
equations of motion can be systematically improved to take into
account higher order gradient corrections [3].

[1]    G. S. Denicol, H. Niemi, in preparation
[2]    G. S. Denicol, H. Niemi, E. Molnar and D. H. Rischke,
        Phys. Rev. D 85, 114047 (2012).
[3]    G. S. Denicol, H. Niemi, I. Bouras, E. Molnar, Z. Xu,
        D. H. Rischke and C. Greiner, arXiv:1207.6811 [nucl-th].