High-T QCD and dimensional reduction: measuring the Debye mass

We study the high-temperature phase of SU(2) and SU(3) QCD using lattice simulations of an effective 3dimensional SU(N) + adjoint Higgs -theory, obtained through dimensional reduction. We investigate the phase diagram of the 3D theory, and find that the high-T QCD phase corresponds to the metastable symmetric phase of the 3D theory. We measure the Debye screening mass mD with gauge invariant operators; in particular we determine the O(g) and O(g) corrections to mD. The corrections are seen to be large, modifying the standard power-counting hierarchy in high temperature QCD.