Zero sound velocity in π, ρ mesons at different temperatures

Sharp transitions are perhaps absent in QCD, so that one looks for physical quantities which may reflect the phase change. One such quantity is the sound velocity which was shown in lattice theory to become zero at the transition point for pure glue. We show that even in a simple bag model the sound velocity goes to zero at temperature T=Tν ≠ 0 and that the numerical value of this Tν depends on the nature of the meson. The average thermal energy of mesons go linearly with T near Tν, with much smaller slope for the pion. The Tν - s can be connected with the Boltzmann temperatures obtained from transverse momentum spectrum of these mesons in heavy ion collision at mid-rapidity. It would be interesting to check the presence of different Tν - s in present day finite T lattice theory. (author). 22 refs, 1 fig., 2 tabs