Yasunori Nomura

Direct-transmission models of dynamical supersymmetry breaking

We systematically construct gauge-mediated supersymmetry- (SUSY-) breaking models with direct transmission of SUSY-breaking effects to the standard-model sector. We obtain a natural model with the gravitino mass m{sub 3/2} smaller than 1 keV as required from the standard cosmology. If all Yukawa coupling constants are of order one, the SUSY-breaking scale m{sub SUSY} transmitted into the standard-model sector is given by m{sub SUSY}{approx_equal}0.1({alpha}{sub i}/4{pi}){Lambda} where {Lambda} is the original dynamical SUSY-breaking scale. Imposing m{sub SUSY}{approx_equal}(10{sup 2}{endash}10{sup 3}) GeV, we get {Lambda}{approx_equal}(10{sup 5}{endash}10{sup 6}) GeV, which yields the gravitino mass m{sub 3/2}{approx_equal}(10{sup {minus}2}{endash}1) keV. {copyright} {ital 1997} {ital The American Physical Society}

Low-scale seesaw mechanisms for light neutrinos

Alternatives to the seesaw mechanism are explored in supersymmetric models with three right-handed or sterile neutrinos. Tree-level Yukawa couplings can be drastically suppressed in a natural way to give sub-eV Dirac neutrino masses. If, in addition, a B −L gauge symmetry broken at a large scale MG is introduced, a wider range of possibilities opens up. The value of the right-handed neutrino mass MR can be easily disentangled from that of MG. Dirac and Majorana neutrino masses at the eV scale can be generated radiatively through the exchange of sneutrinos and neutralinos. Dirac masses mD owe their smallness to the pattern of light-heavy scales in the neutralino mass matrix. The smallness of the Majorana masses mL is linked to a similar seesaw pattern in the sneutrino mass matrix. Two distinct scenarios emerge. In the first, with very small or vanishing MR, the physical neutrino eigenstates are, for each generation, either two light Majorana states with a mixing angle ranging from very small to maximal, depending on the ratio mD/MR, or one light Dirac state. In the second scenario, with a large value of MR, the physical eigenstates are two nearly unmixed Majorana states with masses ∼ mL and ∼ MR. In both cases, the (B−L)-breaking scale MG is, in general, much smaller than that in the traditional seesaw mechanism.

Bimaximal neutrino mixing in SO(10)(GUT)

We find a grand unified SO(10) model which accommodates the bimaximal neutrino mixing for vacuum-oscillation solutions to the atmospheric and solar neutrino problems. This model maintains the original SO(10) mass relation between neutrino and up-type quark masses

Natural effective supersymmetry

{m}_{{\ensuremath{\nu}}_{2}}{/m}_{{\ensuremath{\nu}}_{3}}\ensuremath{\sim}{(m}_{c}{/m}_{t}{)}^{2}.

Quintessence axion potential induced by electroweak instanton effects

Abstract Much heavier sfermions of the first-two generations than the other superparticles provide a natural explanation for the flavor and CP problems in the supersymmetric Standard Model (SUSY SM). However, the heavy sfermions may drive the mass squareds for the light third generation sfermions to be negative through two-loop renormalization group (RG) equations, breaking color and charge. Introducing extra matters to the SUSY SM, it is possible to construct models where the sfermion masses are RG invariant at the two-loop level in the limit of vanishing gaugino-mass and Yukawa-coupling contributions. We calculate the finite corrections to the light sfermion masses at the two-loop level in the models. We find that the finite corrections to the light-squark mass squareds are negative and can be less than (0.3–1)% of the heavy-squark mass squareds, depending on the number and the parameters of the extra matters. We also discuss whether such models realized by the U(1) X gauge interaction at the GUT scale can satisfy the constraints from Δm K and ϵ K naturally. When both the left- and right-handed down-type squarks of the first-two generations have common U(1) X charges, the supersymmetric contributions to Δm K and ϵ K are sufficiently suppressed without spoiling naturalness, even if the flavor-violating supergravity contributions to the sfermion mass matrices are included. When only the right-handed squarks of the first-two generations have a common U(1) X charge, we can still satisfy the constraint from Δm K naturally, but evading the bound from ϵ K requires the CP phase smaller than 10 −2 .

LARGE SQUARK AND SLEPTON MASSES FOR THE FIRST-TWO GENERATIONS IN THE ANOMALOUS U(1) SUSY BREAKING MODELS

The recently observed ultrahigh energy (UHE) cosmic rays beyond the Greisen-Zatsepin-Kuzmin bound can be explained by the decays of some superheavy X particles forming a part of dark matter in our universe. We consider various discrete gauge symmetries

A GAUGE MEDIATION MODEL OF DYNAMICAL SUPERSYMMETRY BREAKING WITHOUT COLOR INSTABILITY

{\mathbf{Z}}_{N}

Gauge-mediation model of dynamical SUSY breaking with a wide range of the gravitino mass

to ensure the required long lifetime

Cosmological Constants as Messenger between Branes

({\ensuremath{\tau}}_{X}\ensuremath{\simeq}{10}^{10}\char21{}{10}^{22}