Implications of the $\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_s$ solution to the atmospheric neutrino anomaly for early Universe cosmology

Abstract

By numerically solving the quantum kinetic equations we compute the range of parameters where the $\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_s$ oscillation solution to the atmospheric neutrino anomaly is consistent with a stringent big bang nucleosynthesis (BBN) bound of $N_{eff}^{BBN}\stackrel{<}{\sim }3.6$. We show that this requires tau neutrino masses in the range $m_{\hat{I}{½}_{\ddot{I}}„}\stackrel{>}{\sim }4eV$ (for $|\hat{I}´m_{atm}^2|=10^{-2.5}e{V}^2$). We discuss the implications of this scenario for hot+cold dark matter, BBN, and the anisotropy of the cosmic microwave background.

some references added and expanded discussion