Measuring the cosmological lepton asymmetry through the cosmic microwave background anisotropy

A large lepton asymmetry in the Universe is still a viable possibility and leads to many interesting phenomena such as gauge symmetry nonrestoration a t high temperature. We show that a large lepton asymmetry changes the predi cted cosmic microwave background (CMB) anisotropy in a dramatic way. Confus ion with other cosmological parameters limits our ability to constrain the lepton asymmetry with current data. However, any degeneracy in the relic ne utrino sea may be measured to a precision of a few percent when the CMB ani sotropy is measured at the: accuracy expected to result from the planned sa tellite missions MAP and Planck.