$\hat{I}{›}_{\mathrm{s}}$CDM cosmology: Alleviating major cosmological tensions by predicting standard neutrino properties

Abstract

We investigate a two-parameter extension of the $\hat{I}{›}_{\mathrm{s}}$CDM model by allowing variations in the effective number of neutrino species $N_{\mathrm{eff}}$ and their total mass $\sum m_{\hat{I}}½$. Our motivation is twofold: (i) to examine whether $\hat{I}{›}_{\mathrm{s}}$CDM retains its success in fitting the data and addressing major cosmological tensions, without suggesting a need for a deviation from the standard model of particle physics, and (ii) to determine whether the data indicate new physics that could potentially address cosmological tensions, either in the post-recombination universe through the late-time mirror AdS-dS transition, or in the pre-recombination universe through modifications in the standard values of $N_{\mathrm{eff}}$ and $\sum m_{\hat{I}}½$, or both. Within the extended $\hat{I}{›}_{\mathrm{s}}$CDM model, referred to as $\hat{I}{›}_{\mathrm{s}}$CDM+$N_{\mathrm{eff}}$+$\sum m_{\hat{\mathrm{I}}½}$, we find no significant tension when considering the Planck-alone analysis. We observe that incorporating BAO data limits the further success of the $\hat{I}{›}_{\mathrm{s}}$CDM extension. However, the weakly model-dependent BAOtr data, along with Planck and Planck+PP\&SH0ES, favor $H_0\sim 73\mathrm{km}{\mathrm{s}}^{-1}\mathrm{Mp}{\mathrm{c}}^{-1}$. In cases where BAOtr dataset is used, the mirror AdS-dS transition is very effective in providing enhanced $H_0$ values, and thus the model requires no significant deviation from the standard value of $N_{\mathrm{eff}}=3.044$. Both the $H_0$ and $S_8$ tensions are effectively addressed, with some compromise in the case of the Planck+BAO dataset. Finally, the upper bounds obtained on $\sum m_{\hat{I}}½\lesssim 0.5$~eV are fully compatible with neutrino oscillation experiments. Our findings provide evidence that late-time physics beyond $\hat{I}›$CDM, such as $\hat{I}{›}_{\mathrm{s}}$CDM, without altering the standard pre-recombination universe, can suffice to alleviate the major cosmological tensions.

24 pages, 6 figures, 3 tables, matches the version published in JCAP