Democratic Universal Seesaw Model with Three Light Sterile Neutrinos

Abstract

Based on the "democratic" universal seesaw model, where mass matrices $M_f$ of quarks and leptons f_i (f=u,d,\nu,e; i=1,2,3) are given by a seesaw form M_f\simeq -m_L M_F^{-1} m_R, and m_L and m_R are universal for all the fermion sectors, and the mass matrices M_F of hypothetical heavy fermions F_i have a democratic structure, a possible neutrino mass matrix is investigated. In the model, there are three sterile neutrinos \nu_{iR} which mix with the active neutrinos \nu_{iL} with \theta \sim 10^{-2} and which are harmless for constraint from the bib bang nucleosynthesis. The atmospheric, solar and LSND neutrino data are explained by the mixings \nu_{\mu L} \leftrightarrow\nu_{\tau L}, \nu_{eL}\leftrightarrow \nu_{eR} and \nu_{eL}\leftrightarrow \nu_{\mu L}, respectively. The model predicts that \Delta m^2_{solar}/\Delta m^2_{atm} \simeq (R^2-1) m_e/\sqrt{m_\mu m_\tau} [R=m(\nu_{iR})/m(\nu_{iL}) (i=1,2,3)] with \sin^{2}2\theta_{atm}\simeq 1 and \Delta m_{LSND}^2/\Delta m^2_{atm} \simeq (1/4)\sqrt{m_\mu/m_e} with \sin^2 2\theta_{LSND} \simeq 4m_e/m_\mu.