eV Seesaw with Four Generations
  We extend the eV seesaw scenario to four lepton generations. The LSND anomaly is taken as the right-handed seesaw scale, i.e. m_R ~ eV. The fourth generation then gives a heavy pseudo-Dirac neutrino which largely decouples from other generations, and is relatively stable. One effectively has a 3+3 solution to the LSND anomaly, where we illustrate with numerical solutions. Our study indicates that the third mixing angle sin^2(theta13) is likely less than 0.01. 
Wei-Shu Hou and Andrea Soddu