3,682 research outputs found
Singlino dominated LSP as CDM candidate in supersymmetric models with an extra U(1)
We consider a singlino dominated neutralino in supersymmetric models with an
extra U(1). In case both the term and also the mass are
generated by the vacuum expectation value of the scalar component of the same
singlet chiral superfield, generically the lightest neutralino is not expected
to be dominated by the singlino. However, if the gaugino corresponding to the
extra U(1) is sufficiently heavy, the lightest neutralino can be dominated by
the singlino and still satisfy the constraints resulting from the
phenomenology. We assume a supersymmetry breaking scenario in which the extra
U(1) gaugino can be much heavier than other gauginos. In that framework we show
that the singlino dominated lightest neutralino may be a good candidate for
dark matter in a parameter space where various phenomenological constraints are
satisfied.Comment: 25 pages, 6 figures, title is changed, introduction is extended,
sec.2 is moved to appendix, some references are added, published versio
The origin of quark and lepton mixings
We propose a model for the mass matrices of quarks and leptons based on two
Abelian flavor symmetries. One is assumed to be broken at a high energy region
near the Planck scale. It is used for the Froggatt-Nielsen mechanism in both
quark and charged lepton sectors. Another one remains unbroken to a multi-TeV
region. The mixings among neutrinos and gauginos including the one of the new
Abelian symmetry generate non-zero masses and mixings among neutrinos. A
bi-maximal scheme for the neutrino oscillation can be realized together with
suitable masses and CKM-mixings in the quark sector. FCNC constraints on this
flavor dependent Abelian symmetry seems to be evaded.Comment: 18 pages, latex, one eps figur
Leptogenesis in a neutrino mass model coupled with inflaton
We propose a scenario for the generation of baryon number asymmetry based on
the inflaton decay in a radiative neutrino mass model extended with singlet
scalars. In this scenario, lepton number asymmetry is produced through the
decay of non-thermal right-handed neutrinos caused from the inflaton decay.
Since the amount of non-thermal right-handed neutrinos could be much larger
than the thermal ones, the scenario could work without any resonance effect for
rather low reheating temperature. Sufficient baryon number asymmetry can be
generated for much lighter right-handed neutrinos compared with the
Davidson-Ibarra bound.Comment: 14 pages, 2 figure
Proton Stability and Small Neutrino Mass in String Inspired Models
We propose a new possibility to realize simultaneously the sufficient proton
stability and the interesting structure of neutrino mass matrix in superstring
inspired models. In this model the leptons and Higgs fields are assigned
to a fundamental representation {\bf 27} in the different way among
generations. Two pairs of Higgs doublets naturally remain light from three
generation ones by imposing certain discrete symmetries, although all extra
color triplets become sufficiently heavy. Under these symmetries suitable
-terms to bring appropriate vacuum expectation values are prepared and the
dangerous FCNC is avoidable. Some related phenomena to this model, especially,
the structure of neutrino mass matrix are also discussed.Comment: 20 pages, latex, a version published in Prog. Theor. Phys.,
discussions related to neutrino masses are change
Strong CP-Problem in Superstring Theory
We apply the solution for the strong CP-problem in the 4-dimensional
superstring theory recently proposed by Ibez and
Lst to Calabi-Yau type models and study its phenomenological
aspects. In Calabi-Yau type models there seem to be phenomenologically
difficult problems in the axion decoupling from the neutral gauge currents and
the compatibility between the proton stability and the cosmological bound on
the axion. DFSZ type invisible axion mechanism which works without heavy extra
colored fields may be more promising than KSVZ axion in the viewpoint of proton
stability.Comment: 11 pages, DPKU920
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