1,389 research outputs found
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 ,
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 . 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 (CB) 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 , and can be as large as
. In particular,
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
CB, 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
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