DPF - PHENO 2024

A Ratio-Preserving Approach to Concordance Cosmology

14 May 2024, 16:15

15m

Barco Law Building 107 (University of Pittsburgh)

Cosmology & Dark Energy Cosmology & Dark Energy

Speaker

Kylar Greene (University of New Mexico)

Description

Cosmological observables are particularly sensitive to key ratios of energy densities and rates, both today and at earlier epochs of the Universe. Well-known examples include the photon-to-baryon and the matter-to-radiation ratios. Equally important, though less publicized, are the ratios of pressure-supported to pressureless matter and the Thomson scattering rate to the Hubble rate around recombination, both of which observations tightly constrain. Preserving these key ratios in theories beyond the $\mathrm{\Lambda }$ Cold-Dark-Matter ($\mathrm{\Lambda }$CDM) model ensures broad concordance with a large swath of datasets when addressing cosmological tensions. We demonstrate that a mirror dark sector, reflecting a partial ${\mathbb{Z}}_2$ symmetry with the Standard Model, in conjunction with percent level changes to the visible fine-structure constant and electron mass which represent a $\mathit{\text{phenomenological}}$ change to the Thomson scattering rate, maintains essential cosmological ratios. Incorporating this ratio preserving approach into a cosmological framework significantly improves agreement to observational data ($\mathrm{\Delta }{\chi }^2=-35.72$) and completely eliminates the Hubble tension with a cosmologically inferred $H_0=73.80\pm 1.02$ km/s/Mpc when including the S$H_0$ES calibration in our analysis. While our approach is certainly nonminimal, it emphasizes the importance of keeping key ratios constant when exploring models beyond $\mathrm{\Lambda }$CDM.

Presentation materials

KylarGreene-DPF-Pheno2024.pdf