Can an SU(2) modification of photon propagation mitigate tensions of ΛCDM?

Janning Meinert

Recent measurements of σ8 from weak lensing follow the trend of increasing tensions between cosmological parameters extracted from different sets of observational data within ΛCDM. In my talk I will subject the CMB to SU(2) Yang-Mills thermodynamics, implying a non-trivial ground state with three thermal phases. For one out of the three thermal phases, the temperature redshift relation is changed. This causes modifications of ΛCDM in particular for high redshifts.

The low-frequency excess of CMB line temperature, as observed by ARCADE 2, can be used to set the Yang-Mills scale. A future blackbody cavity search is discussed in order to probe the existence of the proposed nontrivial ground state physics at low frequencies and low temperatures.

The changed temperature redshift relation together with a quintessence-like transition of dark energy to dark matter produces a CMB fit with H0 in agreement with local observations, a low reionisation redshift of z = 6.23 ± 0.41 and favors a smaller σ8 compared to ΛCDM. However, there is tension with Big Bang Nucleosynthesis due to a significantly lower baryon density.