Derivation of fluid dynamics from the Boltzmann equation, G. Denicol, Frankfurt University, Germany − We present a general derivation of relativistic fluid dynamics from the relativistic Boltzmann equation using the method of moments.  The main difference between our approach and the traditional 14-moment approximation is that we do not close the fluid-dynamical equations of motion by truncating the expansion of the distribution function. Instead, we keep all the terms in the moment expansion and truncate the exact equations of motion for the moments according to a systematic power counting scheme in Knudsen and Reynolds number.  We apply this formalism to obtain an approximate expression for the non-equilibrium single-particle momentum distribution function.  This result is essential to improve the freeze-out description used in the fluid-dynamical modeling of relativistic heavy ion collisions. In order to investigate the implications of our new formalism, we compute the distribution function of a simple system composed of pions, Kaons and nucleons and compare it to the one obtained via the 14-moment approximation.