Neutrinos decoupled from $\beta$-processes and supernova explosion

Based on the gravitational collapse time-scale is larger than the weak interaction time-scale at core densities $\rho >{10}^{11}gr\mathrm{/}{cm}^3$, we approximately use the $\beta$-equilibrium condition and particle number conservations to calculate the number and energy densities of neutrino sphere in the process of gravitational core collapse towards the formation of a proto-neutron star. We find that at core densities $\rho_{dec} > 10^{12} {gr}/ {cm}^{3}$,the$\beta$-equilibrium condition cannot be satisfied consistently with charge, baryon and lepton number conservations, leading to the presence of excess neutrinos decoupling from the $\beta$-equilibrium. These excess neutrinos interact with nucleons and electrons via the neutral current channel only and their diffusion time is about ${10}^{-2}$ sec. The excess neutrino flux could play an important role in an Supernova explosion, provided the fraction of excess neutrinos over all neutrinos is at least one present.