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 $\mu$ term and also the $Z^\prime$ 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 $Z^\prime$ 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

Proton Stability and Small Neutrino Mass in String Inspired E6E_6 Models

We propose a new possibility to realize simultaneously the sufficient proton stability and the interesting structure of neutrino mass matrix in superstring inspired $E_6$ 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 $\mu$-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 Ib${\rm\acute{a}\tilde{n}}$ez and L${\rm\ddot{u}}$st 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

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