Does the CMB prefer a leptonic Universe?

Abstract

Recent observations of the cosmic microwave background (CMB) at smallest angular scales and updated abundances of primordial elements, indicate an increase of the energy density and the helium-4 abundance with respect to standard big bang nucleosynthesis with three neutrino flavour. This calls for a reanalysis of the observational bounds on neutrino chemical potentials, which encode the number asymmetry between cosmic neutrinos and anti-neutrinos and thus measures the lepton asymmetry of the Universe. We compare recent data with a big bang nucleosynthesis code, assuming neutrino flavour equilibration via neutrino oscillations before the onset of big bang nucleosynthesis. We find a slight preference for negative neutrino chemical potentials, which would imply an excess of anti-neutrinos and thus a negative lepton number of the Universe. This lepton asymmetry could exceed the baryon asymmetry by orders of magnitude.

9 pages, 1 figure. v2: added some references. v3: added new data from SPT,ACT,WMAP9, 11 pages, 2 figures, 2 tables, matches for publication accepted version

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Cited by in corpus (14)

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• Boltzmann hierarchy for interacting neutrinos I: formalism
• Leptogenesis and Primordial Magnetic Fields
• Thermodynamics of (2+1)-flavor strongly interacting matter at nonzero isospin
• Flavor versus mass eigenstates in neutrino asymmetries: implications for cosmology
• Updating non-standard neutrinos properties with Planck-CMB data and full-shape analysis of BOSS and eBOSS galaxies
• Probing the properties of relic neutrinos using the cosmic microwave background, the Hubble Space Telescope and galaxy clusters
• Experimental method of detecting relic neutrino by atomic de-excitation
• Prospects for Finding Sterile Neutrino Dark Matter at KATRIN
• Forecast on lepton asymmetry from future CMB experiments
• Spin light of neutrino in astrophysical environments
• Effects of initial spatial phase in radiative neutrino pair emission
• Cosmological chirality and magnetic fields from parity violating particle decays