Gauge Couplings at High Temperature and the Relic Gravitino Abundance

In higher-dimensional supersymmetric theories gauge couplings of the effective four-dimensional theory are determined by expectation values of scalar fields. We find that at temperatures above a critical temperature $T_*$, which depends on the supersymmetry breaking mass scales, gauge couplings decrease like T^{-\a}, \a > 1. This has important cosmological consequences. In particular it leads to a relic gravitino density which becomes independent of the reheating temperature for $T_R > T_*$. For small gravitino masses, m_{3/2} \ll m_{\gl}, the mass density of stable gravitinos is essentially determined by the gluino mass. The observed value of cold dark matter, \O_{\rm CDM}h^2 \sim 0.1, is obtained for gluino masses m_{\gl} = {\cal O}(1 {\rm TeV}).Comment: 11 pages, 2 figures, comment on supersymmetry breaking mechanisms and two references adde

Patterns of remnant discrete symmetries

We analyze patterns of remnant discrete symmetries that arise from U(1)^N theories by spontaneous breaking. We describe a simple, geometrical way to understand these patterns and provide methods for identifying the discrete symmetries and bringing them to the simplest possible form. Applications in GUT and string model building are briefly discussed.Comment: 14 pages, 2 figures, a related Mathematica package can be downloaded from http://einrichtungen.physik.tu-muenchen.de/T30e/codes/DiscreteBreaking

Non-Abelian discrete R symmetries

We discuss non-Abelian discrete R symmetries which might have some conceivable relevance for model building. The focus is on settings with N=1 supersymmetry, where the superspace coordinate transforms in a one-dimensional representation of the non-Abelian discrete symmetry group. We derive anomaly constraints for such symmetries and find that novel patterns of Green-Schwarz anomaly cancellation emerge. In addition we show that perfect groups, also in the non-R case, are always anomaly-free. An important property of models with non-Abelian discrete R symmetries is that superpartners come in different representations of the group. We present an example model, based on a semidirect product of a Z_3 and a Z_8^R symmetry, to discuss generic features of models which unify discrete R symmetries, entailing solutions to the mu and proton decay problems of the MSSM, with non-Abelian discrete flavor symmetries.Comment: 21 page

Non-thermal cosmic neutrino background

We point out that, for Dirac neutrinos, in addition to the standard thermal cosmic neutrino background (C$\nu$B) there could also exist a non-thermal neutrino background with comparable number density. As the right-handed components are essentially decoupled from the thermal bath of standard model particles, relic neutrinos with a non-thermal distribution may exist until today. The relic density of the non-thermal (nt) background can be constrained by the usual observational bounds on the effective number of massless degrees of freedom $N_\mathrm{eff}$, and can be as large as $n_{\nu_{\mathrm{nt}}}\lesssim 0.5\,n_\gamma$. In particular, $N_\mathrm{eff}$ can be larger than 3.046 in the absence of any exotic states. Non-thermal relic neutrinos constitute an irreducible contribution to the detection of the C$\nu$B, and, hence, may be discovered by future experiments such as PTOLEMY. We also present a scenario of chaotic inflation in which a non-thermal background can naturally be generated by inflationary preheating. The non-thermal relic neutrinos, thus, may constitute a novel window into the very early universe.Comment: 6 pages, 2 figure

Baryogenesis From Flavon Decays

Many popular attempts to explain the observed patterns of fermion masses involve a flavon field. Such weakly coupled scalar fields tend to dominate the energy density of the universe before they decay. If the flavon decay happens close to the electroweak transition, the right-handed electrons stay out of equilibrium until the sphalerons shut off. We show that an asymmetry in the right-handed charged leptons produced in the decay of a flavon can explain the baryon asymmetry of the universe

The LMA Solution from Bimaximal Lepton Mixing at the GUT Scale by Renormalization Group Running

We show that in see-saw models with bimaximal lepton mixing at the GUT scale and with zero CP phases, the solar mixing angle theta_{12} generically evolves towards sizably smaller values due to Renormalization Group effects, whereas the evolution of theta_{13} and theta_{23} is comparatively small. The currently favored LMA solution of the solar neutrino problem can thus be obtained in a natural way from bimaximal mixing at the GUT scale. We present numerical examples for the evolution of the leptonic mixing angles in the Standard Model and the MSSM, in which the current best-fit values of the LMA mixing angles are produced. These include a case where the mass eigenstates corresponding to the solar mass squared difference have opposite CP parity.Comment: 14 pages, 10 figures; references and a subsection containing an example with odd CP parities added; results and conclusions unchange