Neutrino mixing schemes and neutrinoless double beta decay
  We study the possible structure of the neutrino mass matrix taking into consideration the solar and atmospheric neutrinos and the neutrinoless double beta decay. We emphasize on mass matrices with vanishing elements. There are only a very few possibilities remaining at present. We concentrate on three generation scenarios and find that with three parameters there are few possibilities with and without any vanishing elements. For completeness we also present a five parameter four neutrino (with one sterile neutrino) mass matrix which can explain all these experiments and the LSND result. 
H.V. Klapdor-Kleingrothaus (MPI, Heidelberg) and U. Sarkar   (Visva-Bharati Univ, Santiniketan, India)