Dirac neutrino masses with Planck scale lepton number violation

Abstract

The natural occurrence of Dirac neutrino masses at low energies in presence of Planck scale lepton number was described. The occurrence of Dirac neutrino masses was obtained by breaking lepton number on Planck brane while right-handed (RH) neutrino was localized on the TeV brane in 5D frame. The small Dirac Yukawa coupling was obtained by small wave function overlap. The RH neutrino was identified as composite CFT bound state and lepton number violation was suppressed by conformal field theory (CFT) operators in 4D frame.