Observational Constraints on Early Coupled Quintessence

Abstract

We investigate an Early Coupled Quintessence model where a light scalar mediates a fifth force stronger than gravity among dark matter particles and leads to the growth of perturbations prior to matter-radiation equality. Using cosmological data from the $\text{Planck}$ Cosmic Microwave Background power spectra, the Pantheon+ Type 1a Supernovae, Baryon Acoustic Oscillations, and Big Bang Nucleosynthesis, we constrain the coupling strength ${\hat{I}}^2$ and the redshift $z_{\mathrm{OFF}}$ at which the interaction becomes effectively inactive, finding a firm degeneracy between these two parameters which holds true regardless of when the scaling regime begins.

12 pages, 10 figures