Democratic universal seesaw model with three light sterile neutrinos

Based on the `democraticʹ universal seesaw model, where mass matrices Mf of quarks and leptons fi (f=u,d,ν,e; i=1,2,3) are given by a seesaw form Mf≃−mLMF−1mR, and mL and mR are universal for all the fermion sectors, and the mass matrices MF of hypothetical heavy fermions Fi have a democratic structure, a possible neutrino mass matrix is investigated. In the model, there are three sterile neutrinos νiR which mix with the active neutrinos νiL with θ∼10−2 and which are harmless for constraint from the big bang nucleosynthesis. The atmospheric, solar and the LSND neutrino data are explained by the mixings νμL↔ντL, νeL↔νeR and νeL↔νμL, respectively. The model predicts that Δm2solar/Δm2atm≃(R2−1)me/mμmτ [R=m(νiR)/m(νiL) (i=1,2,3)] with sin22θatm≃1 and ΔmLSND2/Δm2atm≃(1/4)mμ/me with sin22θLSND≃4me/mμ.