SU(2)$_{\rm CMB}$ and the cosmological model: angular power spectra

Abstract

Driven by the CMB temperature-redshift ($T$-$z$) relation as demanded by deconfining SU(2) Yang-Mills thermodynamics, an according cosmological model is proposed and analysed. This model -- SU(2)$_\CMB$ -- exhibits a dark sector, representing $\Lambda$CDM with a certain late-time dark-matter density which transitions to a reduced (present-day) density parameter at high $z$. We statistically analyse constraints on cosmological parameters directly imposed by the values of the standard co-moving ruler $r_d$ and the angular size of the sound horizon $\theta_*$. Compared to the $\Lambda$CDM best fit to 2015 Planck data, we require an increased (present-day) dark matter density when $r_d\cdot H_0=$\,const and a value $H_0\sim 73.5$ km\,s$^{-1}$Mpc$^{-1}$ -- typical for local extractions -- are used. The ratio between the density parameters of primordial and late-time dark matter ranges between 0.5 and 0.7. We confirm this trend by fitting the predictions of SU(2)$_\CMB$, obtained from a modified CLASS code, to the angular power spectra TT, TE, and EE. We consider adiabatic, scalar primordial curvature perturbations and distinguish two treatments of thermal quasi-particles in the perturbation equations. Best fits predict a red-tilted primordial power spectrum. Moreover, a low baryon density is obtained compared with the coincidence value of BBN, the $\Lambda$CDM best fit of the 2015 Planck data, and the observed deuterium abundance. Our derived values of $H_0$ support the results of local cosmological observations. Also, there is a tendency for late reionisation.