We discuss the postulate that the U(1) gauge group describing photon propagation results from a dynamically broken SU(2) gauge theory. In the context of Yang-Mills thermodynamics such a symmetry breaking occurs via the nontrivial ground state. As a result of the interaction with the quasi particles of the theory the photon acquires an effective, temperature and momentum dependent, mass. We explain how this leads to modified black body spectra at temperatures of about 5 K. Furthermore, we discuss the properties and effects of an emergent longitudinal polarization.In this section we briefly repeat some key results of the non-perturbative approach to SU(2)Yang-Mills thermodynamics. Based on these results, we state a postulate, from which these results have direct relevance to a gas of photons. A detailed derivation and discussion can be found in [1], and an overview in last year's ICNAAM presentations [2].In Yang-Mills thermodynamics, calorons of trivial [3] and nontrivial [4,5] holonomy are non-perturbative, finite action solutions to the equations of motion. By performing a spatial average over non-interacting calorons [6], the non-perturbative ground-state can be described by a macroscopic adjoint scalar field φ with modulus |φ | = Λ 3 /2πT . Here, T and Λ denote the temperature and Yang-Mills scale, respectively. The field φ does not fluctuate and acts as a background for the topological trivial sector of the theory [7].The investigation of propagating gauge modes is done by a transformation to unitary gauge [7]. It is then seen that the SU(2)-symmetry is dynamically broken down to U(1) by φ . The theory then contains one tree-level massless (TLM) mode interacting with two tree-level heavy (TLH) modes. The mass of the latter is given by m = 2e |φ | and depends on temperature. The effective gauge coupling e(T ) is a function of temperature, and exhibits a logarithmic pole at the critical temperature T c = 13.87Λ/2π as well as a plateau value of √ 8π for T Λ. In spite of this large value for the coupling constant a loop expansion of thermodynamical quantities shows rapid conversion due to compositeness constraints [8].
POSTULATE ABOUT PHOTONS AND SU(2) CMBAlthough massless on tree-level, the calculation of the one-loop polarization tensor of the TLM mode [9] reveals that it acquires a temperature dependent mass, due to the interaction with the TLH modes. But since the mass of the TLH modes diverges at T c , they decouple from the TLM mode at this temperature. This implies that the TLM mode is exactly massless at T c only. It is this property that allows for a connection to photon physics via the following postulate [7]. Namely, the photon is postulated to be the TLM mode of a new gauge group, called SU(2) CMB . To determine the value of T c , we note that the cosmic microwave background radiation, as the prime example of a thermalized photon gas, exhibits an almost perfect black body spectrum. This then gives T c ≡ T CMB 2.73 K. A more detailed discussion on the value of T c can be found in [1]. Another important ...