Testing the fundamental physical properties of relic neutrinos using cosmological data

Abstract

In this thesis we investigate the observational constraints on the cosmic neutrino background (CNB) given by the extended ΛCDM scenario (ΛCDM +Nef f + P mν + c 2 ef f + c 2 vis + ξν) using the latest observational data from Planck CMB (temperature power spectrum, low-polarisation and lensing reconstruction), baryon acoustic oscillations (BAOs), the new recent local value of the Hubble constant from Hubble Space Telescope (HST) and information of the abundance of galaxy clusters (GCs). We study the constraints on the CNB background using CMB + BAO + HST data with and without the GC data. We find ∆Nef f = 0.614 ± 0.26 at 68 per cent confidence level when the GC data are added in the analysis. We do not find significant deviation for sound speed in the CNB rest frame. We also analyze the particular case ΛCDM +Nef f + P mν +ξν with the observational data. Within this scenario, we find ∆Nef f = 0.60 ± 0.28 at 68 per cent confidence level. In both the scenarios, no mean deviations are found for the degeneracy parameter. On the other hand, We consider a cosmological lepton asymmetry in the form of neutrinos and impose new expected sensitivities on such asymmetry through the degeneracy parameter (ξν) by using some future CMB experiment configurations, such as CORE and CMB-S4. Taking the default scenario with three neutrino states, we find ξµ = 0.05 ± 0.10 (± 0.04), from CORE (CMB-S4) at 95 percent CL, respectively. Also, within this scenario, we evaluate the neutrino mass scale, obtaining that the normal hierarchy mass scheme is privileged. Our results are an update concerning on the cosmological lepton asymmetry and the neutrino mass scale within this context, from which can bring a perspective on the null hypothesis for ξν (and its effects on ∆Nef f ), where perhaps, ξν may take a non-null value up to 95 percent CL from future experiments such as CMB-S4. Finally, we consider the possibility of testing new thermalized light particles and also constraints possible new-physics interactions of Dirac neutrinos. Many Dirac-neutrino models that aim to address the Dirac stability, the smallness of neutrino masses, or the matter–anti-matter asymmetry of our Universe confer the right-handed chirality partners νR with additional interactions that can thermalize them, which is the case of ultralight Z’ bosons. We discuss well-motivated models for νR interactions such as gauged U(1)B−L, through measure of the effective number of relativistic degrees of freedom in the early Universe, Nef f . We consider an extension of the standard model of cosmology, type ΛCDM + Σmν + M 0 z , where M 0 z is the mass of the Z’ boson. Using different observational tests, we found that P mν < 0.32 eV, Mz 0 < 17.2 GeV and meff ν,sterile < 0.47 eV, which is within the limits of previous studies, including the 2018 results of the Planck collaboration. Furthermore, we compare the sensitivity of SPT-3G, Simons Observatory, and CMB-S4 to other experiments, in particular the LHC.