Quintessential cosmological tensions

Abstract

Several cosmological tensions have emerged in light of recent data, most notably in the inferences of the parameters ${H}_{0}$ and ${\ensuremath{\sigma}}_{8}$. We explore the possibility of alleviating both these tensions simultaneously by means of the Albrecht-Skordis ``quintessence'' potential. The field can reduce the size of the sound horizon ${r}_{s}^{*}$ while concurrently suppressing the power in matter density fluctuations before it comes to dominate the energy density budget today. Interestingly, this rich set of dynamics is governed entirely by one free parameter that is of $\mathcal{O}(10)$ in Planck units. We find that the inferred value of ${H}_{0}$ can be increased, while that of ${\ensuremath{\sigma}}_{8}$ can be decreased, both by $\ensuremath{\approx}1\ensuremath{\sigma}$ compared to the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ case. However, ultimately the model is disfavored by Planck and BAO data alone, compared to the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model, with a $\mathrm{\ensuremath{\Delta}}{\ensuremath{\chi}}^{2}\ensuremath{\approx}+6$. When including large scale structure and supernova data we find $\mathrm{\ensuremath{\Delta}}{\ensuremath{\chi}}^{2}\ensuremath{\approx}+1$. We note that historically much attention has been focused on preserving the three angular scales ${\ensuremath{\theta}}_{D}$, ${\ensuremath{\theta}}_{\mathrm{EQ}}$, and ${\ensuremath{\theta}}_{s}^{*}$ to their $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ values. Our work presents an example of how, while doing so indeed maintains a relatively good fit to the cosmic microwave background data for an increased number of ultrarelativistic species, it is a priori insufficient in maintaining such a fit in more general model spaces.