Large solar angle and see-saw mechanism: a bottom-up perspective

In addition to the well established large atmospheric angle, a large solar angle is probably present in the leptonic sector. In the context of the see-saw and by means of a bottom-up approach, we explore which patterns for the Dirac and Majorana right-handed mass matrices provide two large mixings in a robust way and with the minimal amount of tuning. Three favorite patterns emerge, which have a suggestive physical interpretation in terms of the role played by right-handed neutrinos: in both solar and atmospheric sectors, either a single or a pseudo-Dirac pair of right-handed neutrinos dominates. Each pattern gives rise to specific relations among the neutrino mixing angles and mass differences, which lead to testable constraints on U-e3. The connection with the rate of LFV charged lepton decays is also addressed. (C) 2002 Published by Elsevier Science B.V.