Thermal QCD sum rules in the ρ0 channel revisited

From the hypothesis that at zero temperature the square root of the spectral continuum threshold s(0) is linearly related to the QCD scale Lambda we derive in the chiral limit and for temperatures considerably smaller than Lambda scaling relations for the vacuum parts of the Gibbs averaged scalar operators contributing to the thermal operator product expansion of the rho (0) current-current correlator. The scaling with lambda drop roots(0)(T)/s(0)(0), s(0) being the T-dependent perturbative QCD continuum threshold in the spectral integral, is simple for renormalization group invariant operators, and becomes nontrivial for a set of operators which mix and scale anomalously under a change of the renormalization point. In contrast to previous works on thermal QCD sum rules with this approach the gluon condensate exhibits a sizable T-dependence. The rho -meson mass is found to rise slowly with temperature which coincides with the result found by means of a PCAC and current algebra analysis of the rho (0) correlator.