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

Abstract In this work, we investigate a two-parameter extension of the Λ s CDM 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 (∑ m ν ). Our motivation is twofold: (i) to examine whether the Λ s CDM 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 s CDM 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 s CDM model, referred to as Λ s CDM+ 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 s CDM 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. Our findings provide evidence that late-time physics beyond ΛCDM, such as Λ s CDM, without altering the standard description of the pre-recombination universe, can suffice to alleviate the major cosmological tensions, as indicated by our analysis of Λ s CDM+ N eff +∑ m ν .