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 at high temperature. We show that a large lepton asymmetry changes the predicted cosmic microwave background (CMB) anisotropy in a dramatic way. Confusion with other cosmological parameters limits our ability to constrain the lepton asymmetry with current data. However, any degeneracy in the relic neutrino sea may be measured to a precision of a few percent when the CMB anisotropy is measured at the accuracy expected to result from the planned satellite missions MAP and Planck. 1999