Applications of Chiral Symmetry

I discuss several topics in the applications of chiral symmetry at nonzero temperature. First, where does the rho go? The answer: up. The restoration of chiral symmetry at a temperature Tχ implies that the ρ and a1 vector mesons are degenerate in mass. In a gauged linear sigma model the ρ mass increases with temperature, mρ(Tχ) > mρ(0). I conjecture that at Tχ the thermal ρ− a1 peak is relatively high, at about ∼ 1GeV , with a width approximately that at zero temperature (up to standard kinematic factors). The ω meson also increases in mass, nearly degenerate with the ρ, but its width grows dramatically with temperature, increasing to at least ∼ 100MeV by Tχ. I also stress how utterly remarkable the principle of vector meson dominance is, when viewed from the modern perspective of the renormalization group. Secondly, I discuss the possible appearance of disoriented chiral condensates from “quenched” heavy ion collisisons. It appears difficult to obtain large domains of disoriented chiral condensates in the standard two flavor model. This leads to the last topic, which is the phase diagram for QCD with three flavors, and its proximity to the chiral critical point. QCD may be very near this chiral critical point, and one might thereby generated large domains of disoriented chiral condensates. Based upon talks presented at the “Workshop on Finite Temperature QCD and Quark-Gluon Transport Theory”, Wuhan, PRC, April, 1994