Particle theory

Abstract:

We review a class of supersymmetric models in which the light neutrino masses result from higher-dimensional supersymmetry-breaking terms in the MSSM super- and Kähler-potentials. The mechanism used in these models is closely related to the Giudice-Masiero mechanism for the MSSM μ parameter and leads to TeV-scale right-handed neutrino and sneutrino states. In these models, the dominant contribution to the light neutrino (Majorana) mass matrix is a one-loop term with a sub-dominant tree-level "seesaw" contribution. It is also shown that it is possible to construct a natural model of TeV-scale leptogenesis via the resonant behavior of the one-loop self-energy contribution to the right-handed neutrino (Ni) decay. This model addresses the primary problems of previous phenomenological studies of low-energy leptogenesis: a rational for TeV-scale right-handed neutrinos with small Yukawa couplings; the origin of the tiny, but non-zero mass splitting required between at least two Ni masses; and the necessary non-trivial breaking of flavor symmetries in the right-handed neutrino sector. © World Scientific Publishing Company.

Abstract:

Following Freivogel et al we consider inflation in a predictive (or 'friendly') region of the landscape of string vacua, as modeled by Arkani-Hamed, Dimopoulos and Kachru. In such a region the dimensionful coefficients of super-renormalizable operators unprotected by symmetries, such as the vacuum energy and scalar mass-squareds are freely scanned over, and the objects of study are anthropically or 'environmentally' conditioned probability distributions for observables. In this context we study the statistical predictions of (inverted) hybrid inflation models, where the properties of the inflaton are probabilistically distributed. We derive the resulting distributions of observables, including the deviation from flatness |1-Ω|, the spectral index of scalar cosmological perturbations ns (and its scale dependence dns/dlog k), and the ratio of tensor to scalar perturbations r. The environmental bound on the curvature implies a solution to the η-problem of inflation with the predicted distribution of (1-n s) indicating values close to current observations. We find a relatively low probability (< 3%) of 'just-so' inflation with measurable deviations from flatness. Intermediate scales of inflation are preferred in these models. © SISSA 2006.

Abstract:

The transport properties of certain strongly coupled thermal gauge theories can be determined from their effective description in terms of gravity or superstring theory duals. Here we provide a short summary of the results for the shear and bulk viscosity, charge diffusion constant, and the speed of sound in supersymmetric strongly interacting plasmas. We also outline a general algorithm for computing transport coefficients in any gravity dual. The algorithm relates the transport coefficients to the coefficients in the quasinormal spectrum of five-dimensional black holes in asymptotically anti de Sitter space.