Constraints on neutrino degeneracy from the cosmic microwave background and primordial nucleosynthesis

Abstract

We reanalyze the cosmological constraints on the existence of a net universal lepton asymmetry and neutrino degeneracy based upon the latest high resolution CMB sky maps from BOOMERANG, DASI, and MAXIMA-1. We generate likelihood functions by marginalizing over (Ω b h 2 , ξν µ,τ , ξν e , ΩΛ, h, n) plus the calibaration uncertainties. We consider flat ΩM + ΩΛ = 1 cosmological models with two identical degenerate neutrino species, ξν µ,τ ≡ |ξν µ | = |ξν τ | and a small ξν e . We assign weak top-hat priors on the electron-neutrino degeneracy parameter ξν e and Ω b h 2 based upon allowed values consistent with the nucleosynthesis constraints as a function of ξν µ,τ . The change in the background neutrino temperature with degeneracy is also explicitly included, and Gaussian priors for h = 0.72±0.08 and the experimental calibration uncertainties are adopted. The marginalized likelihood functions show a slight (0.5σ) preference for neutrino degeneracy. Optimum values with two equally degenerate µ and τ neutrinos imply ξν µ,τ = 1.

Primordial density perturbation in the curvaton scenario

“…In that case BBN and CMB/LSS together give constraints on |ξ µ | = |ξ τ | (assumed equal for convenience) and ξ e which are much weaker, namely |ξ µ,τ | ≤ 2.5 and |ξ e | ≤ 0.30 [42]. Note that these limits were obtained assuming a purely adiabatic primordial perturbation spectrum and hence serve only as a rough guide in the case of a correlated curvature and neutrino isocurvature perturbations.…”

“…If the favoured large mixing angle (LMA) solution to the solar neutrino problem is correct, neutrino oscillations ensure that the ξ i have a common value ξ [41] . In that case, the BBN/LSS constraint is [42] −0.01 < ξ < 0.07. With this constraint, unperturbed lepton number densities are almost certainly too small to have any observable effect on the CMB anisotropy or large-scale structure (LSS).…”

Present Status of Primordial Nucleosynthesis After Wmap: Results From a New BBN Code

“…a renewed attention in the last few years [23], [61]- [65]. The bounds from BBN and CMB data on the asymmetry parameters ξ α for the three active neutrinos, α = e, µ, τ , are more stringent by considering the effect of oscillations in primordial universe.…”

WMAP five-year constraints on lepton asymmetry and radiation energy density: implications for Planck

“…The density perturbations in leptonic asymmetric cosmological models have been discussed in literature [59,60,45,46,63,64]. We applied them to modify the Boltzmann Code for Anisotropies in the Microwave Background (CAMB) [65,66,67] to compute the CMB temperature and polarization anisotropies power spectra and LSS matter density fluctuations power spectra for the case of three degenerated neutrinos/antineutrinos with the total mass m ν and degeneracy parameter ξ ν .…”