Connecting bimaximal neutrino mixing to a light sterile neutrino

It is shown that if small neutrino masses owe their origin to the conventional seesaw mechanism and the MNS mixing matrix is in the exact bimaximal form, then there exist symmetries in the theory that allow one of the righthanded neutrinos to become naturally massless, making it a candidate for the sterile neutrino discussed in the literature. Departures from the exact bimaximal limit leads to tiny mass for the sterile neutrino as well as its mixing to the active neutrinos. This provides a minimal theoretical framework where a simultaneous explanation of the solar, atmospheric and LSND observations within the so-called 3+1 scenario may be possible.Comment: new references added; paper accepted for publication in Phys. Rev. D.(rapid communications); note adde

Three-dimensional computed tomography cephalometry of plagiocephaly: Asymmetry and shape analysis

Copyright © 2006 The American Cleft Palate-Craniofacial AssociationObjectiveTo investigate facial asymmetry associated with both deformational and synostotic plagiocephaly and to identify variables based on skeletal landmarks that distinguish the conditions and quantify severity.DesignRetrospective, cross sectional.SettingAustralian Craniofacial Unit, Adelaide.Main outcome measuresProportional differences between bilateral distances and principal component (PC) analysis of the skeletal landmarks.PatientsThe three-dimensional positions of 78 osseous landmarks were determined from computed tomography (CT) scans of 21 patients with deformational plagiocephaly (DP), 20 patients with unilateral coronal synostosis (UCS), and 2 patients with unilateral lambdoid synostosis (ULS).ResultsFor both DP and UCS, significant asymmetry was found for the orbital depths, mandibular lengths, maxillary depths, zygomatic arch lengths, lateral base of the parietal bone, and the angle between the anterior and the posterior cranial base projected onto the axial plane. The small sample size for ULS precluded definitive statistical statements but allowed some useful comparisons with the other conditions. The first three PC scores were able to distinguish among the three conditions and which side was affected.ConclusionsThe asymmetry of the cranial base and facial structures, arising from localized abnormality or deformational forces in either the frontal or the occipital regions, can be quantified by a plethora of bilateral features or summarized by PC analysis.D.J. Netherway, A.H. Abbott, N. Gulamhuseinwala, K.L. McGlaughlin, P.J. Anderson, G.C. Townsend, D.J. Davi