Limiting temperature of pion gas with the van der Waals equation of state

Abstract

The grand canonical ensemble formulation of the van der Waals equation of state that includes the effects of Bose statistics is applied to the equilibrium system of interacting pions. If the attractive interaction between pions is large enough, a limiting temperature T0 emerges, i.e., no thermodynamical equilibrium is possible at . The system pressure p, particle number density n, and energy density ε remain finite at , whereas for T near T0 both the specific heat and the scaled variance of particle number fluctuations are proportional to and, thus, go to infinity at . The limiting temperature also corresponds to the softest point of the equation of state, i.e., the speed of sound squared goes to zero as . Very similar thermodynamical behavior takes place in the Hagedorn model for the special choice of a power, namely , in the pre-exponential factor of the mass spectrum .