Large Mixing from Small: Pseudo-Dirac Neutrinos and the Singular Seesaw

Abstract

If the sterile neutrino mass matrix in an otherwise conventional seesaw model has a rank less than the number of flavors, it is possible to produce pseudo-Dirac neutrinos. In a two-flavor, sterile rank 1 case, we demonstrate analytic conditions for large active mixing induced by the existence of (and coupling to) the sterile neutrino components. For the three-flavor, rank 1 case, ``3+2'' scenarios with large mixing also devolve naturally as we show by numerical examples. We observe that, in this approach, small mass differences can develop naturally without any requirement that masses themselves are small. Additionally, we show that significant three channel mixing and limited experimental resolution can combine to produce extracted two channel mixing parameters at variance with the actual values.

26pp., 3 figs., revtex4; extension of hep-ph/0307245

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• Multichannel oscillations and relations between LSND, KARMEN and MiniBooNE, with and without CP violation
• Large Mixing Angle Sterile Neutrinos and Pulsar Velocities
• Pseudo-Dirac Neutrinos and Relic Neutrino Matter Effect on the High-energy Neutrino Flavor Composition
• Sterile Neutrinos in a 6x6 Matrix Approach