  We derive an a useful priori estimate for the thermal ground state of
deconfining phase of SU(2) Yang-Mills thermodynamics in four-dimensional, flat
spacetime and discuss its implications. Upon a selfconsistent spatial
coarse-graining over noninteracting, trivial-holonomy (BPS saturated)
(anti)calorons of unit topological charge modulus an inert, adjoint scalar
field $|\phi|$ and an effective pure-gauge configuration $a_\mu^{gs}$ emerge.
The modulus $|\phi|>0$ defines the maximal resolution in the coarse-grained
theory and induces dynamical gauge-symmetry breaking. Thanks to perturbative
renormalizability and the fact that |phi| can not absorb or emit
energy-momentum the effective action is local and simple. The temperature
dependence of the effective coupling is a consequence of thermodynamical
consistency and describes the Coulomb screening of a static test charge due to
short-lived monopole-antimonopole pairs. The latter occur unresolvably as
small-holonomy excitations of (anti)calorons by the absorption of propagating
fundamental gauge fields.
