The effect of medium on the relaxation of the dissipative flows in an interacting pion gas

Abstract

Through the last decade the experimental results from high energy nucleus nucleus collisions have proved to be extremely useful to characterize the thermodynamic properties of the strongly interacting system created in these collisions. Hydrodynamic simulations have been used effectively to describe the space-time evolution of the collisions at RHIC and LHC. Ideal hydrodynamics does not suffice to explain the elliptic flow (v2) data of charged hadrons at RHIC and demands the inclusion of dissipative dynamics to describe the space-time evolution of the system. Since then the study of non-equilibrium processes have assumed a great deal of importance in the analyses of heavy ion collisions. The dissipative processes within a system are quantified through the transport coefficients. The first order theories of relativistic dissipative fluid dynamics, in which the thermodynamic fluxes are linearly related to the thermodynamic forces involves the shear and bulk viscosities and thermal conductivity. However since the first order theory does not contain any time derivative of the corresponding fluxes, it results in the equations of motions that are parabolic in structure. This leads to the undesirable feature of acausality which results in infinite speed of the flows, making it impossible to estimate the relaxation times of the flows. This requires the use of a second order theory which produces hyperbolic equations of motions, leading to finite time scale over which the dissipative fluxes de-