报告题目：QCD thermodynamics at intermediate coupling

报 告 人：苏楠，德国Bielefeld大学

报告时间：9月11日下午15：45-17：00

报告地点：物理系三楼报告厅

报告摘要：The weak-coupling expansion of the QCD free energy is known to the order g^6*log[g], however, the resulting series is poorly convergent at phenomenologically relevant temperatures. In the first part of this talk, 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 HTLpt results of QCD thermodynamics to 3-loop order, which 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 could be used to calculate static and dynamic quantities for temperatures relevant at LHC. In the second part of this talk, I will move on to discuss the effect of the gauge fixing ambiguity, i.e. the Gribov copies, on the thermodynamic quantities. I will report the motivation and progress of a 1-loop Yang-Mills thermodynamics calculation with the Gribov copies fixed. The Gribov mass parameter can be solved self-consistently via a non-perturbative horizon condition and the result turns out to be of the order g^2T, i.e. the same order as the magnetic scale. As a consequence, the 1-loop thermodynamic potential already contains contributions from the non-perturbative magnetic scale. In contrast to the conventional Faddeev-Popov gauge fixing case where the vacuum part is discarded in the normalization, there are scale dependent divergences coming from the vacuum part which have to be regularized. As a result, fixing the Gribov copies may provide a perturbative scheme which is able to incorporate (part of) the non-perturbative magnetic contributions.