We study the $\nu_{ \mu}$ and $\nu_{ \tau}$ decays in the early epoch of the universe. If $m_{ \nu_{ \tau}}>2m_e$, there would be a CP asymmetry between $\nu_{ \tau}\rightarrow e^++e^-+\nu_e$ and $\bar{ \nu}_{ \tau} \rightarrow e^++e^-+\bar{ \nu}_e$. 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 $m_{ \nu_{ \tau}}>2m_{ \mu}\sim 200$ MeV, the CP non-invariance can be much larger.
Categories: hep-ph