Neutrino oscillation based on a $\sim$ 10 eV neutrino

We study a consistent explanation for both deficits of solar neutrino and atmospheric neutrino due to the neutrino oscillation induced by the mixing of five light neutrinos with a heavy right-handed neutrino. Although this scenario contains only one nonzero mass eigenvalue \sim 10~eV for these five neutrino states, it can consistently explain both deficiency. It can also naturally present a suitable hot dark matter candidate as its own feature. We propose a phenomenological model for the neutrino mass matrix which realizes such a scenario in the simple three generation left and right handed neutrino framework.