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A Ratio-Preserving Approach to Cosmological Concordance

Tuesday April 9, 2024
2:00 pm

 Presenter:  Kylar Greene (UNM & Fermilab)
 Series:  Nuclear, Particle, Astroparticle and Cosmology (NUPAC) Seminars
 Abstract:  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 $Lambda$ Cold-Dark-Matter ($Lambda$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 textit{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 ($Deltachi^2=-35.72$) 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 $Lambda$CDM.
 Web Site:    https:/ / unm.zoom.us/ j/ 94141126387
 Location:  Zoom

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