Measuring the cosmological lepton asymmetry through the CMB anisotropy

TL;DR

This paper demonstrates that large lepton asymmetry significantly affects CMB anisotropy predictions and can be precisely measured by upcoming satellite missions, providing stronger constraints than primordial nucleosynthesis.

Contribution

It shows how lepton asymmetry impacts CMB anisotropy and forecasts measurement precision with future satellite data.

Findings

Current measurements already constrain lepton asymmetry more tightly than nucleosynthesis.

Future CMB observations will measure relic neutrino degeneracy to 1% accuracy.

Large lepton asymmetry influences gauge symmetry at high temperatures.

Abstract

A large lepton asymmetry in the Universe is still a viable possibility and leads to many interesting phenomena such as gauge symmetry nonrestoration at high temperature. We show that a large lepton asymmetry changes the predicted cosmic microwave background (CMB) anisotropy and that any degeneracy in the relic neutrino sea will be measured to a precision of 1% or better when the CMB anisotropy is measured at the accuracy expected to result from the planned satellite missions MAP and Planck. In fact, the current measurements already put an upper limit on the lepton asymmetry of the Universe which is stronger than the one coming from considerations of primordial nucleosynthesis and structure formation.