Transport Coefficients of Hadronic Matter

Ultra-relativistic heavy-ion collisions at RHIC are thought to have created a Quark-Gluon-Plasma (QGP) with a very low shear viscosity in the deconfined phase. However, as the QGP hadronizes it will evolve through a hadronic phase with rapidly increasing viscosity. In order to fully characterize the QGP state, one has to separately determine the viscosity of the hadronic phase. We present a calculation of transport coefficients such as the shear viscosity, the shear viscosity to entropy density ratio $\frac{\eta}{s}$, and the diffusion coefficient as a function of $T$ and $\mu_B$ for nuclear densities in the range $(\rho_0 - 2 \rho_0)$. The hadronic medium is simulated using the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model in a box with periodic boundary conditions. Green-Kubo theory enables us to compute linear transport coefficients of such a medium by examining near-equilibrium fluctuations. We outline a scheme combining the Green-Kubo formalism and our microscopic transport model to extract the time-dependence of the shear viscosity of the matter created in an ultrarelativistic heavy ion collision.