Phase Transition in Hot Pion Matter

Abstract

The equation of state for the pion gas is analyzed within the third virial approximation. The second virial coefficient is found from the pion-pion- scattering data, while the third one is considered as a free parameter. The proposed model leads to a first-order phase transition from the pion gas to a more dense phase at the temperature T_pt < 136 MeV. Due to relatively low temperature this phase transition cannot be related to the deconfinement. This suggests that a new phase of hadron matter - 'hot pion liquid' - may exist.Comment: 11 pages, Latex, 4 PS-figures. V2: A few misprints are corrected. Acknowledgments are adde