Neutrino oscillation based on the mixings with a heavy right-handed 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 light neutrinos with a heavy right-handed neutrino. We propose such a phenomenological neutrino mass matrix that realizes this scenario in the simple three generation left- and right- handed neutrino framework. Although this model contains only one nonzero mass eigenvalue similar to 10 eV for these light neutrino states at the first approximation level, it can be expected to explain consistently both deficiencies due to the appropriate higher order corrections. A suitable hot dark matter candidate is naturally included in it as its own feature.