Entropy Production in Relativistic Hydrodynamics

The entropy production occurring in relativistic hydrodynamical systems such as the quark-gluon plasma (QGP) formed in high-energy nuclear collisions is explored. We study mechanisms which change the composition of the fluid, i.e. particle production and/or chemical reactions, along with chemoand thermo-diffusion. These effects complement the conventional dissipative effects of shear viscosity, bulk viscosity, and heat conductivity. Introduction. There is fundamental interest in the study of high energy density matter, which promises to illucidate further the properties of the strongly interacting vacuum and the high temperature phases of strongly interacting matter [1, 2]. The method of choice for the description of the rapidly evolving and possibly inhomogeneous quark-gluon plasma (QGP) has been often the hydrodynamical approach [3, 4]. It is generally believed that QGP existed shortly after the Big Bang initial phase of the universe, and that it may be re-created in relativistic nuclear collisions [5, 6]. In order to gain a better understanding of this new form of matter, we explore here the entropy production due to numerous dissipative effects arising in the evolution of QGP towards the point of hadronization. The entropy content of the QGP phase at hadronization determines the observable particle multiplicity [7]. Therefore, in order to establish via particle multiplicity the initial conditions reached in heavy-ion collisions [3], the effect of entropy production in QGP evolution has to be understood. To begin with, we present here the main result of this paper, before embarking on its derivation. The entropy production is given by: T∂μs μ = − ∑