Cosmological lepton asymmetry with a nonzero mixing angle \theta_{13}

TL;DR

This paper investigates how the neutrino mixing angle  affects cosmological bounds on lepton asymmetry, showing that larger  tightens these bounds and forecasting future improvements from COrE data.

Contribution

It provides new limits on relic neutrino asymmetries considering flavor oscillations and different  values, and forecasts future constraints from CMB experiments.

Findings

Larger  values lead to more stringent neutrino asymmetry limits.

Current bounds are dominated by Big Bang Nucleosynthesis constraints.

Future CMB experiments could improve limits by up to a factor of 6.6.

Abstract

While the baryon asymmetry of the Universe is nowadays well measured by cosmological observations, the bounds on the lepton asymmetry in the form of neutrinos are still significantly weaker. We place limits on the relic neutrino asymmetries using some of the latest cosmological data, taking into account the effect of flavor oscillations. We present our results for two different values of the neutrino mixing angle \theta_{13}, and show that for large \theta_{13} the limits on the total neutrino asymmetry become more stringent, diluting even large initial flavor asymmetries. In particular, we find that the present bounds are still dominated by the limits coming from Big Bang Nucleosynthesis, while the limits on the total neutrino mass from cosmological data are essentially independent of \theta_{13}. Finally, we perform a forecast for COrE, taken as an example of a future CMB experiment, and find that it could improve the limits on the total lepton asymmetry approximately by up to a factor 6.6.