Modified Boltzmann Transport Equation and Freeze Out

Abstract.We study the Freeze-Out process in high-energy heavy-ion reaction. The description of the process is based on the Boltzmann Transport Equation (BTE). We point out the basic limitations of the BTE approach and introduce the Modified BTE. The Freeze-Out dynamics is presented in the 4-dimensional space-time in a layer of finite thickness, and we employ the Modified BTE for the realistic Freeze-Out description.