  In this work, we study the appearance of neutrino asymmetries during the
expansion of the Universe. A mathematical model based on differential equations
was used to describe the processes of neutrino oscillations considering CP
violation and neutrino collisions. An analysis of the emergence of neutrino
asymmetry due to collisions of neutrinos with each other and due to CP
violation during neutrino oscillations is presented. It was discovered that the
asymmetry bifurcates into two states with positive and negative asymmetry for
the inverse hierarchy of neutrino masses. A state with a normal hierarchy of
neutrino masses is unstable and is not realized. It is shown that the maximum
CP violation is realized. The influence of this process on the dispersion of
the primordial $^4\text{He}$ mass fraction is calculated, which is confirmed by
astrophysical observations. Thus, the inverse hierarchy of neutrino masses is
realized. The CP violation in neutrino oscillations is maximum and the phase is
$\delta_{13}=270^\circ (-\pi/2)$
