String inspired neutrino mass textures in light of KamLAND and WMAP

Recent data from astrophysical and terrestrial experiments indicates large mixing angles in the neutral lepton sector and restricts the allowed regions of neutrino masses. In particular, the large mixing angles in the lepton sector are disparate from the small mixing in the quark sector. This disparity is unnatural from the point of view of grand unified theories, that are well motivated by the Standard Model multiplet structure and logarithmic running of its parameters. we examine the issue of this disparity from the perspective of string derived SO(10) GUT models, in which the SO(10) symmetry is broken directly at the string theory level. A characteristic feature of such models is the appearance of numerous SO(10) singlet fields. We propose that the mismatch between the quark and lepton mixing parameters arises due to this extended singlet spectrum and its mixing with the right-handed neutrinos. We discuss a string inspired effective parameterization of the extended neutrino mass matrix and demonstrates that the coupling with the SO(10) singlet spectrum can readily account for the neutrino flavor parameters. The mechanism implies that some SO(10) singlet fields should exist at intermediate mass scales. We study the possibility of deriving the neutrino mass spectrum from string theory in a specific string derived vacuum solution, and comment on the properties that such a solution should possess. (C) 2003 Elsevier B.V. All rights reserved.