John March-Russell

Abstract:

We show that the recently constructed 5-dimensional supersymmetric S 1 /(Z2 × Z′2) orbifold GUT models allow an appealing explanation of the observed hierarchical structure of the quark and lepton masses and mixing angles. Flavor hierarchies arise from the geometrical suppression of some couplings when fields propagate in different numbers of dimensions, or on different fixed branes. Restrictions arising from locality in the extra dimension allow interesting texture zeroes to be easily generated. In addition the detailed nature of the SU(5)-breaking orbifold projections lead to simple theories where b - τ unification is maintained but similar disfavored SU(5) relations for the lighter generations are naturally avoided. We find that simple 5d models based on S1 /(Z2 × Z′2) are strikingly successful in explaining many features of the masses and mixing angles of the 2nd and 3rd generation. Successful three generation models of flavor including neutrinos are constructed by generalizing the S1 /(Z2 × Z′2) model to six dimensions. Large angle neutrino mixing is elegantly accommodated. Novel features of these models include a simple mu = 0 configuration leading to a solution of the strong CP problem. © SISSA/ISAS 2004.

Abstract:

This biennial Review summarizes much of Particle Physics. Using data from previous editions, plus 1726 new measurements from 512 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. Among the 119 reviews are many that are new or heavily revised including those on neutrino mixing, CP violation in K, D, and B mesons, Vcb, the new exotic Θ(1540) particle, extra-dimensions, grand unified theories, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology. A booklet is available containing the Summary Tables and abbreviated versions ofsome of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http//pdg.lbl.gov. ©2004 Regents of the University of California.

Abstract:

We propose a model of TeV-scale resonant leptogenesis based upon recent models of the generation of light neutrino masses from supersymmetry-breaking effects with TeV-scale right-handed (rhd) neutrinos, Ni The model leads to large cosmological lepton asymmetries via the resonant behaviour of the one-loop self-energy contribution to Ni decay. Our model addresses the primary problems of previous phenomenological studies of low-energy leptogenesis: a rational for TeV-scale rhd neutrinos with small Yukawa couplings so that the out-of equilibrium condition for Ni decay is satisfied; the origin of the tiny, but non-zero mass splitting required between at least two Ni masses; and the necessary non-trivial breaking of flavour symmetries in the rhd neutrino sector. The low mass-scale of the rhd neutrinos and their superpartners, and the TeV-scale A-terms automatically contained within the model offer opportunities for partial direct experimental tests of this leptogenesis mechanism at future colliders. © SISSA/ISAS 2004.