Constraining neutrino physics with BBN and CMBR
S. H. Hansen, G. Mangano, A. Melchiorri, G. Miele, O. Pisanti
TL;DR
This study tests the consistency between CMBR observations from BOOMERanG and DASI and Standard BBN predictions by jointly constraining the baryon density $Ω_b h^2$ and the effective number of neutrino species $N_ν$ via a likelihood framework. It extends the analysis to Degenerate BBN by allowing nonzero neutrino chemical potentials $ξ_e$, $ξ_{μ}$, and $ξ_{τ}$ and combines CMBR with BBN and SNIa priors to bound $N_ν$ and the lepton asymmetries. The joint analysis yields $Ω_b h^2 ≈ 0.019$ and $N_ν ≈ 2.8$ (95% CL), in good agreement with SBBN, and places tight limits on $ξ_e$ and $ξ_{μ,τ}$ (e.g., $-0.01 ≤ ξ_e ≤ 0.22$ and $|ξ_{μ,τ}| ≤ 2.6$ with certain priors). Overall, the results support the standard cosmological model while constraining possible beyond-Standard-Model neutrino physics, highlighting the critical role of the CMBR third peak in reducing parameter degeneracies.
Abstract
We perform a likelihood analysis of the recent results on the anisotropy of Cosmic Microwave Background Radiation from the BOOMERanG and DASI experiments to show that they single out an effective number of neutrinos in good agreement with standard Big Bang Nucleosynthesis. We also consider degenerate Big Bang Nucleosynthesis to provide new bounds on effective relativistic degrees of freedom $N_ν$ and, in particular, on neutrino chemical potential $ξ_α$. When including Supernova Ia data we find, at $2σ$, $N_ν\leq 7$ and $-0.01 \leq ξ_e \leq 0.22$, $|ξ_{μ,τ}|\leq 2.6$.