2,538 research outputs found
Gravitino Production from Heavy Moduli Decay and Cosmological Moduli Problem Revived
The cosmological moduli problem for relatively heavy moduli fields is
reinvestigated. For this purpose we examine the decay of a modulus field at a
quantitative level. The modulus dominantly decays into gauge bosons and
gauginos, provided that the couplings among them are not suppressed in the
gauge kinetic function. Remarkably the modulus decay into a gravitino pair is
unsuppressed generically, with a typical branching ratio of order 0.01. Such a
large gravitino yield after the modulus decay causes cosmological difficulties.
The constraint from the big-bang nucleosynthesis pushes up the gravitino mass
above 10^5 GeV. Furthermore to avoid the over-abundance of the stable
neutralino lightest superparticles (LSPs), the gravitino must weigh more than
about 10^6 GeV for the wino-like LSP, and even more for other neutralino LSPs.
This poses a stringent constraint on model building of low-energy
supersymmetry.Comment: 14 pages, 1 figure; minor correction
Splitting Triplet and Doublet in Extra Dimensions
A novel mechanism to realize the triplet-doublet splitting in supersymmetric
SU(5) grand unified theories is proposed in the framework of higher dimensional
theories where chiral multiplets are localized due to kink configuration of a
SU(5) singlet. An adjoint Higgs field which spontaneously breaks the SU(5)
gauge symmetry is assumed to be involved with the localization process,
splitting the wave functions of the color-triplet Higgs from its doublet
counterpart. The resulting effective four-dimensional theory does not possess
manifest SU(5) invariance. By adjusting couplings, the doublet mass can be
exponentially suppressed. We also show that dimension 5 proton decay from
triplet Higgs exchange can be suppressed to a negligible level.Comment: 9 pages, 2 figures, some references adde
Hadronic Axion Model in Gauge-Mediated Supersymmetry Breaking
A simple hadronic axion model is proposed in the framework of gauge-mediated
supersymmetry breaking. Dynamics of Peccei-Quinn symmetry breaking is governed
by supersymmetry breaking effects and the Peccei-Quinn breaking scale
is inversely proportional to the gravitino mass. The gravitino mass range which
corresponds to the axion window GeV -- GeV
lies in the region predicted by gauge-mediated supersymmetry breaking models.
The model is also shown to be cosmologically viable.Comment: 20 pages including seven postscript figures, reviced version to be
published in Physics Letters
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