Λ_sCDM cosmology: alleviating major cosmological tensions by predicting standard neutrino properties

In this work, we investigate a two-parameter extension of the Λ_sCDM model, as well as the ΛCDM model for comparison, by allowing variations in the effective number of neutrino species (N _eff) and their total mass (∑mν). Our motivation is twofold: (i) to examine whether the Λ_sCDM framework 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 (z ∼ 2) mirror AdS-to-dS transition feature of the Λ_sCDM model, or in the pre-recombination universe through modifications in the standard values of N _eff and ∑m_ν , or both. Within the extended Λ_sCDM model, referred to as Λ_sCDM+N _eff+∑m_ν , we find no significant tension when considering the Planck-alone analysis. We observe that incorporating BAO data limits the further success of the Λ_sCDM extension. However, the weakly model-dependent BAOtr data, along with Planck and Planck+PP&SH0ES, favor an H ₀ value of approximately 73 km s^-1 Mpc^-1, which aligns perfectly with local measurements. In cases where BAOtr is part of the combined dataset, 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 _eff = 3.044, remaining consistent with the standard model of particle physics. 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 total neutrino mass, ∑m_ν ≲ 0.50 eV, are fully compatible with neutrino oscillation experiments.