John March-Russell

Abstract:

Recently, the HESS telescope has observed a gamma-ray spectrum from the galactic center extending to at least $\sim$10 TeV. Although it has been suggested that this could be the product of annihilating dark matter particles, the candidates most frequently discussed (such as neutralinos) are far too light to account for this flux. In this letter, we consider stable particles from the messenger sector of gauge mediated supersymmetry breaking models as an alternative dark matter candidate. We find that a 20 to 30 TeV messenger state can provide a thermal relic density consistent with the measured dark matter density of the universe and can indeed generate the spectrum observed by HESS.

Abstract:

The inferred values of the cosmological baryon and dark matter densities are strikingly similar, but in most theories of the early universe there is no true explanation of this fact; in particular, the baryon asymmetry and thus density depends upon unknown, and {\it a priori} unknown and possibly small, CP-violating phases which are independent of all parameters determining the dark matter density. We consider models of dark matter possessing a particle-antiparticle asymmetry where this asymmetry determines both the baryon asymmetry and strongly effects the dark matter density, thus naturally linking $\Omega_{\rm{b}}$ and $\Omega_{\rm{dm}}$. We show that sneutrinos can play the role of such dark matter in a previously studied variant of the MSSM in which the light neutrino masses result from higher-dimensional supersymmetry-breaking terms.

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.