Improved constraints on lepton asymmetry from the cosmic microwave background

Abstract

A cosmic lepton asymmetry ${\eta }_{\text{l}}=(n_{\text{l}}-n_{\bar{\text{l}}})/n_{\gamma }$ affects the primordial helium abundance and the expansion rate of the early Universe. Both of these effects have an impact on the anisotropies of the cosmic microwave background (CMB). We derive constraints on the neutrino chemical potentials from the Planck 2015 data, assuming equal lepton flavour asymmetries and negligible neutrino masses. We find $\xi =-0.002_{-0.111}^{+0.114}$ (95\% CL) for the chemical potentials, which corresponds to $-0.085\le {\eta }_{\text{l}}\le 0.084$. Our constraints on the lepton asymmetry are significantly stronger than previous constraints from CMB data analysis and we argue that they are more robust than those from primordial light element abundances. The resulting constraints on the primordial helium and deuterium abundances are consistent with those from direct measurements.

6 pages, 3 figures; extended discussion about the literature, accepted by EPL

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Cited by in corpus (6)

• How to relax the cosmological neutrino mass bound
• Probing the properties of relic neutrinos using the cosmic microwave background, the Hubble Space Telescope and galaxy clusters
• Lepton Flavour Asymmetries and the Mass Spectrum of Primordial Black Holes
• Effects of the QCD Equation of State and Lepton Asymmetry on Primordial Gravitational Waves
• A review of neutrino decoupling from the early universe to the current universe
• Lepton Number and Expansion of the Universe