Maximal atmospheric neutrino mixing in an SU(5) modelW. Grimus1 and L. Lavoura2
1 Universität Wien, Institut für Theoretische Physik, Boltzmanngasse 5, 1090 Wien, Austria
2 Universidade Técnica de Lisboa, Centro de Física das Interacções Fundamentais, Instituto Superior Técnico, 1049-001 Lisboa, Portugal
(Received: 29 November 2002 / Published online: 3 March 2003)
We show that maximal atmospheric and large solar neutrino mixing can be implemented in SU(5) gauge theories, by making use of the U(1)F symmetry associated with a suitably defined family number F, together with a symmetry which does not commute with F. U(1)F is softly broken by the mass terms of the right-handed neutrino singlets, which are responsible for the seesaw mechanism; in addition, U(1)F is also spontaneously broken at the electroweak scale. In our scenario, lepton mixing stems exclusively from the right-handed-neutrino Majorana mass matrix, whereas the CKM matrix originates solely in the up-type-quark sector. We show that, despite the non-supersymmetric character of our model, unification of the gauge couplings can be achieved at a scale ; indeed, we have found a particular solution to this problem which yields results almost identical to the ones of the minimal supersymmetric standard model.
© Società Italiana di Fisica, Springer-Verlag 2003