Applications of QCD sum rules at finite temperature

Abstract

QCD sum-rule techniques are applied to the spectra of $\ensuremath{\rho}$ and $\frac{J}{\ensuremath{\psi}}$ mesons at finite temperature to investigate the relative importance of quark and gluon condensates and perturbative thermal effects in determining bound-state parameters. Of particular interest are the consequences of nonperturbative physics persisting above the deconfinement phase transition, which is implied by nonzero gluon condensates found in lattice calculations. For the $\ensuremath{\rho}$ meson, the quark thermal bath induces only a smooth variation in the hadronic parameters as the temperature is increased; the quark condensate and its temperature dependence are the most important factors. For the $\frac{J}{\ensuremath{\psi}}$ meson, perturbative thermal effects overwhelm the gluon condensate contribution at a temperature around 100 MeV, so that high-temperature charmonium physics is consistent with that expected in a weakly interacting quark-gluon plasma. Corrections to other plasma properties from nonperturbative physics are discussed.