Mirror Dark Sector Solution of the Hubble Tension with Time-varying Fine-structure Constant by John Zhang et al. on Wednesday 30 November

We explore a model introduced by Cyr-Racine, Ge, and Knox

(arXiv:2107.13000(2)) that resolves the Hubble tension by invoking a ``mirror

world" dark sector with energy density a fixed fraction of the ``ordinary"

sector of Lambda-CDM. Although it reconciles cosmic microwave background and

large-scale structure observations with local measurements of the Hubble

constant, the model requires a value of the primordial Helium mass fraction

that is discrepant with observations and with the predictions of Big Bang

Nucleosynthesis (BBN). We consider a variant of the model with standard Helium

mass fraction but with the value of the electromagnetic fine-structure constant

slightly different during photon decoupling from its present value. If $\alpha$

at that epoch is lower than its current value by $\Delta \alpha \simeq -2\times

10^{-5}$, then we can achieve the same Hubble tension resolution as in

Cyr-Racine, et al. but with consistent Helium abundance. As an example of such

time-evolution, we consider a toy model of an ultra-light scalar field, with

mass $m <4\times 10^{-29}$ eV, coupled to electromagnetism, which evolves after

photon decoupling and that appears to be consistent with late-time constraints

on $\alpha$ variation.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.03236v2