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Noriyuki Oshimo

Publications and source records attributed to Noriyuki Oshimo.

At least 37 records · Page 2Linked to original sources
arXiv1999

A Supersymmetric Model with an Extra U(1) Gauge Symmetry

In the standard model the proton is protected from decay naturally by gauge symmetries, whereas in the ordinary minimal supersymmetric standard model an ad hoc discrete symmetry is imposed for the proton stability. We present a new supersymmetric model in which the proton decay is forbidden by an extra U(1) gauge symmetry. Particle contents are necessarily increased to be free from anomalies, incorporating right-handed neutrinos. Both Dirac and Majorana masses are generated for neutrinos, yielding non-vanishing but small masses. The superpotential consists only of trilinear couplings and the mass parameter $μ$ of the minimal model is induced by spontaneous breaking of the U(1) symmetry.

hep-ph↗
arXiv1999

CP asymmetry for radiative B-meson decay in the supersymmetric standard model

We study a rate asymmetry in the inclusive decay $\Bsgamma$, assuming the supersymmetric standard model based on N=1 supergravity. A complex coefficient $A$ for scalar-trilinear couplings is the source of CP violation, which is contained in the mass-squared matrices for squarks. The model parameters are nontrivially constrained by experimental results for the branching ratio of the radiative decay and for the electric dipole moments of the neutron and the electron. The decay rate asymmetry is predicted to be much larger than that by the standard model in a wide region of the parameter space compatible with the experiments. Its magnitude can be maximally around 0.1, which will be well accessible at B factories.

hep-ph↗
arXiv1999

CP-odd WWZ couplings induced by vector-like quarks

A minimal extension of the standard model includes extra quarks with charges 2/3 and/or -1/3, whose left-handed and right-handed components are both SU(2) singlets. This model predicts new interactions of flavor-changing neutral current at the tree level, which also violate CP invariance. We study CP-odd anomalous couplings for the gauge bosons W, W, and Z induced by the new interactions at the one-loop level. These couplings become nonnegligible only if both an up-type and a down-type extra quarks are incorporated. Their form factors are estimated to be maximally of order $10^{-5}$. Such magnitudes are larger than those predicted in the standard model, though smaller than those in certain other models.

hep-ph↗
arXiv1998

Decay rate asymmetry in $B \to X_s γ$ as a signature of supersymmetry

In the supersymmetric standard model, the radiative $B$-meson decay $B \to X_s γ$ could receive a large contribution from a new source of flavor-changing neutral current, which also violates CP invariance. The CP-conjugate processes then may sizably differ in decay width. If a new CP-violating phase is not suppressed, this decay rate asymmetry can be significantly larger than the prediction by the standard model, possibly detectable at B factories. Such a large asymmetry may be implied by the measured branching ratio which is consistent with the standard model.

hep-ph↗
arXiv1998

Decay Rate Asymmetry of Top Squark

We discuss a decay rate asymmetry of the top squark, which is induced by a new source of CP violation intrinsic in the supersymmetric standard model. Although new sources of CP violation in this model are severely constrained from the electric dipole moment of the neutron, an unsuppressed CP-violating phase can still coexist with a top squark whose mass is accessible by near-future colliders. Then the dominant decay mode of the top squark has a width different from its CP conjugate process. The magnitude of this $CP$ asymmetry becomes of order $10^{-3}$.

hep-ph↗
arXiv1998

Baryon asymmetry and neutron EDM

Baryon asymmetry of the universe can be generated by new sources of $CP$ violation intrinsic in supersymmetric extension of the standard model. This scenario predicts the neutron electric dipole moment to be not much smaller than its present experimental upper bound.

hep-ph↗
arXiv1998

Baryogenesis from top squark transport

Baryon asymmetry of the universe is generated in the supersymmetric standard model (SSM) through the charge transport mechanism mediated by top squarks. Necessary CP violation originates from a complex phase contained in mass-squared matrices of squarks and sleptons. This complex phase also gives contributions to the electric dipole moments (EDMs) of the neutron and the electron. The amount of induced baryon asymmetry is consistent with its observed value within reasonable ranges of SSM parameters. The EDMs are predicted to be slightly smaller than their experimental upper limits.

hep-ph↗
arXiv1998

CP violation in the top-quark system through light squarks

We study a decay rate asymmetry of the top quark in the supersymmetric standard model, taking into account the constraints from the electric dipole moments of the neutron and the electron. One CP-violating phase contained in the mass-squared matrices of squarks and sleptons is allowed to have an unsuppressed value, even if their masses are of order 100 GeV. Sizable $CP$ violation could then occur in the production and decay of the top quark through interactions with top squarks. The asymmetry between the widths for the decays $t\to bW^+$ and $\bar t\to \bar bW^-$ can be of order $10^{-3}$, which will possibly be detectable in the near future.

hep-ph↗
arXiv1997

CP-odd Anomalous W-boson Couplings from Supersymmety

The supersymmetric standard model contains a new CP-violating phase in the mass matrices for charginos and neutralinos, which could induce CP-odd anomalous couplings for the WWZ and WWγvertices at the one-loop level. We study these couplings, paying attention to the model-parameter and q^2 dependencies. It is shown that the CP-odd form factors could have values of order 10^{-3}-10^{-4}, which are much larger than those predicted by the standard model. We also discuss the possibility of examining these form factors in experiments.

hep-ph↗
arXiv1997

Study of CP Violation: Electroweak Baryogenesis and Anomalous W-Boson Couplings

The contributions from the Ochanomizu CP Study Group to the KEK meetings on "CP violation and its origin" (1993-1997) are summarized on electroweak baryogenesis and anomalous W-boson couplings. We survey planned new experiments which could examine some aspects studied in our contributions. We also discuss several issues on baryogenesis. Ten problems are presented for further studies.

hep-ph↗
arXiv1997

Electric Dipole Moments of Neutron and Electron in Supersymmetric Model

The electric dipole moments (EDMs) of the neutron and the electron are reviewed within the framework of the supersymmetric standard model (SSM) based on grand unified theories coupled to N=1 supergravity. Taking into account one-loop and two-loop contributions to the EDMs, we explore SSM parameter space consistent with experiments and discuss predicted values for the EDMs. Implications of baryon asymmetry of our universe for the EDMs are also discussed.

hep-ph↗
arXiv1997

Implications of baryon asymmetry for the electric dipole moment of the neutron

We study baryogenesis at the electroweak phase transition of the universe within the framework of the supersymmetric standard model (SSM) based on N=1 supergravity. This model contains a new source of CP violation in the mass-squared matrices for squarks, which could enable $t$ squarks to mediate the charge transport mechanism for generating baryon asymmetry. The same CP-violating source also induces the electric dipole moment (EDM) of the neutron at the one-loop level. If the new CP-violating phase is not suppressed, it is shown, the $t$-squark transport can lead to baryon asymmetry consistent with its observed value within reasonable ranges of SSM parameters. For these parameter ranges the magnitude of the neutron EDM is predicted to be not much smaller than its present experimental upper bound.

hep-ph↗
arXiv1997

Electric dipole moments of W boson and neutron from supersymmetry

The supersymmetric standard model (SSM) has a CP-violating phase in its gauge-Higgs sector. This new source of CP violation induces the electric dipole moments (EDMs) of the neutron and electron at the one-loop level. The same CP-violating phase generates the EDM of the $W$ boson through one-loop diagrams mediated by the charginos and neutralinos, which leads to the EDMs of the neutron and electron at the two-loop level. We discuss these EDMs, assuming that the CP-violating phase has the magnitude of order 0.1--1 which may be suggested from the baryon asymmetry of the universe. Even at the two-loop level the neutron and the electron could have EDMs which are smaller than their experimental upper bounds by only one order of magnitude. Since these two-loop contributions do not depend on the values of SSM parameters for the squark or slepton sector, they provide predictions for the EDMs less ambiguous than the one-loop contributions.

hep-ph↗
arXiv1996

Electroweak baryogenesis from chargino transport in the supersymmetric model

We study the baryon asymmetry of the universe in the supersymmetric standard model (SSM). At the electroweak phase transition, the fermionic partners of the charged SU(2) gauge bosons and Higgs bosons are reflected from or transmitted to the bubble wallof the broken phase. Owing to a physical complex phase in their mass matrix, these reflections and transmissions have asymmetries between CP conjugate processes. Equilibrium conditions in the symmetric phaseare then shifted to favor a non-vanishing value for the baryon number density, which is realized through electroweak anomaly. We show that the resultant ratio of baryon number to entropy is consistent with its present observed value within reasonable ranges of SSM parameters, provided that the CP-violating phase intrinsic in the SSM is not much suppressed. The compatibility with the constraints on the parameters from the electric dipole moment of the neutron is also discussed.

hep-ph↗
arXiv1996

Neutron Electric Dipole Moment from Supersymmetric Anomalous W-boson Coupling

In the supersymmetric standard model (SSM) the $W$-boson could have a non-vanishing electric dipole moment (EDM) through a one-loop diagram mediated by the charginos and neutralinos. Then the $W$-boson EDM induces the EDMs of the neutron and the electron. We discuss these EDMs, taking into consideration the constraints from the neutron and electron EDMs at one-loop level induced by the charginos and squarks or sleptons. It is shown that the neutron and the electron could respectively have EDMs of order of $10^{-26}e$cm and $10^{-27}e$cm, solely owing to the $W$-boson EDM. Since these EDMs do not depend on the values of SSM parameters for the squark or slepton sector, they provide less ambiguous predictions for CP violation in the SSM.

hep-ph↗
arXiv1995

Signatures of Supersymmetry at B-Factories

We discuss CP asymmetries in $B^0$-meson decays and \BsBs mixing within the framework of the supersymmetric standard model (SSM). It is shown that \BdBd and \KK mixings could receive sizable new contributions through box diagrams mediated by the charginos and charged Higgs bosons. This implies that the CP-violating phase of the Cabibbo-Kobayashi-Maskawa matrix may have a value which is different from the one predicted by the standard model (SM). The value of the CP-violating phase affects the amounts of the CP asymmetries and \BsBs mixing. We examine predictions for these quantities in both the SSM and the SM, exploring the difference between the two models.

hep-ph↗
arXiv1994

$CP$ violation in minimal supersymmetric standard model

$CP$ violating phenomena predicted by the minimal supersymmetric standard model are discussed in a case where the $CP$ violating phases in SUSY sector are not suppressed. The electric dipole moments of the neutron and the electron are large, but can be smaller than their experimental upper bounds if the scalar quarks and leptons are heavier than a few TeV. $T$ violating asymmetries in the production processes of the different neutralino pair and the different chargino pair emerge at the tree level. They could be as large as of order $10^{-2}$ in unpolarized electron beam experiments and $10^{-1}$ in polarized electron beam experiments. In a pair production of the charginos of the same mass, the asymmetry emerges through the electric and the weak "electric" dipole moments of the charginos at the loop level, but its magnitude is at most of order $10^{-4}$.

hep-ph↗