2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/46162We study the $ν_μ$ and $ν_τ$ decays in the early epoch of the universe. If $m_{ν_τ}>2m_e$, there would be a CP asymmetry between $ν_τ\rightarrow e^++e^-+ν_e$ and $\barν_τ \rightarrow e^++e^-+\barν_e$. The resultant CP non-invariance is a function of temperature and density and can reach $10^{-7}$ for a reasonable temperature range, but it is noticed that if $m_{ν_τ}>2m_μ\sim 200$ MeV, the CP non-invariance can be much larger.14 pages(LaTeX), uuencode, 2 figures(1 PS file)High Energy Physics - Phenomenologytext