The deconfining phase of SU(2) Yang-Mills thermodynamics

We present an overview on nonperturbative thermodynamics in the deconfining phase of an SU(2) Yang-Mills theory. In a unique effective theory the maximal resolution of trivial-topology fluctuations is constrained by coarse-grained, interacting calorons and anticalorons. Loop expansions of thermodynamical quantities are discussed. Postulating that SU(2)$_{\tiny{CMB}}\stackrel{\tiny{today}}=U(1)_Y$, a modification of thermalized, low-momentum photon propagation is predicted for temperatures a few times that of the cosmic microwave background. We discuss phenomenological implications: magnetic-field induced dichroism and birefringence at a temperature of 4.2 K (PVLAS), stability of cold and dilute clouds of atomic hydrogen in our galaxy, and absence of low-$l$ correlations in the TT CMB power spectrum.