Nan Su, Bielefeld University
QCD Thermodynamics at Intermediate Coupling

Abstract: The weak-coupling expansion of the QCD free energy is known
to order g6*log[g],  however,  the resulting series is poorly
convergent at phenomenologically relevant temperatures. I will discuss
how the gauge invariant hard-thermal-loop perturbation theory (HTLpt)
reorganization of the calculation improves the convergence of the
successive approximations to the QCD free energy. I will present new
results of an HTLpt calculation of QCD thermodynamics to three loops.
The results of this calculation are consistent with lattice data down
to 2-3T_c. This is a non-trivial result since,  in this temperature
regime,  the QCD coupling constant is neither infinitesimally weak nor
infinitely strong with g~2,  or equivalently alpha_s~0.3. Therefore,
we have a crucial test of the quasiparticle picture in the
intermediate coupling regime. Our results suggest that HTLpt provides
a systematic framework that can be used to calculate static and
dynamic quantities for temperatures relevant at LHC.