Particle theory

Abstract:

Two ground-based experiments have recently independently detected TeV γ-rays from the direction of the galactic centre. The observations made by the VERITAS and CANGAROO collaborations are unexpected, although not impossible to interpret in terms of astrophysical sources. Here we examine in detail whether the observed γ-rays may arise from the more exotic alternative of annihilations of dark matter particles clustered in the centre of the galaxy. ©2004 IOP Publishing Ltd.

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.