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Noriyuki Oshimo

Publications and source records attributed to Noriyuki Oshimo.

At least 19 recordsLinked to original sources
arXiv2019

Electric dipole moment of the electron in the model with extra Higgs bosons

The Higgs sector which is extended from the standard model could generally become an origin of CP violation. In the model with two doublet and one triplet Higgs fields on SU(2) symmetry, we study the electric dipole moment (EDM) of the electron whose non-vanishing value has not yet been established experimentally. The Higgs potential is assumed to be consistent with supersymmetric theory, though supersymmetric particles are not taken into consideration explicitly. While the parameter values of the model are severely constrained by the properties of the observed Higgs boson, certain ranges lead to a magnitude for the electron EDM around the experimental upper bound. Signatures of the extra Higgs bosons in collision experiments are discussed briefly.

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arXiv2015

Higgs bosons in supersymmetric model with CP-violating potential

In the supersymmetric standard model which is not minimal, the Higgs potential does not conserve CP symmetry generally. Assuming that there exists an SU(2)-triplet Higgs field, we discuss resultant CP-violating effects on the Higgs bosons. The experimentally observed Higgs boson, which should be CP-even in the standard model, could decay into two photons of CP-odd polarization state non-negligibly. For the second lightest Higgs boson, in sizable region of parameter space, the dominant decay modes are different from those expected by the standard model. The two-photon decay could yield both even and odd CP final states at a ratio of oder of unity.

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arXiv2012

Coexistence of CP eigenstates in Higgs boson decay

The supersymmetric extension of the standard model contains an intrinsic sourceof CP violation mediated by the charginos. As an effect, both CP-even and CP-odd final states could be observed in the Higgs boson decay into two photons whose evidences were reported recently.

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arXiv2009

Realistic model for SU(5) grand unification

A grand unified model based on SU(5) and supersymmetry is presented. Pairs of superfields belonging to 15 and 15* representations are newly introduced, while gauge coupling unification is satisfied. Improper mass relations in the minimal model between charged leptons and d-type quarks are corrected. Neutrinos have non-vanishing masses, with large angles for generation mixings of the leptons being compatible with the small angles of the quarks. Constraints from proton decay are relaxed. A new source for lepton number generation in the early universe is provided.

hep-ph↗
arXiv2006

Generation Mixing of Sneutrinos in Heavier Chargino Decay

The heavier chargino decay could yield two charged leptons of different generations, owing to generation mixing of sneutrinos. We discuss the possibility of producing $e$ and $μ$ through this process in near future collider experiments. The analyses are made systematically in the supersymmetric extension of the standard model without assuming a specific scenario for the mixing. Production of the heavier chargino is evaluated in $e^+e^-$ collisions. In the parameter region consistent with nonobservation of the radiative $μ$ decay, sizable parts lead to a detectable branching ratio for the generation-changing decay of the heavier chargino.

hep-ph↗
arXiv2004

Generation-changing interaction of sneutrinos in $e^+e^-$ collisions

Measurability of generation mixing is studied on the pair production of sneutrinos in $e^+e^-$ collisions and their subsequent decays into two different charged leptons $e$ and $μ$ with two lighter charginos. The analyses are made systematically in a general framework of the supersymmetric extension of the standard model. The production and decay process depends on the parameters of the chargino sector, as well as those of the sneutrino sector. Although generation-changing interactions are severely constrained by radiative charged-lepton decays, sizable regions in the parameter space could still be explored at $e^+e^-$ colliders in near future.

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arXiv2003

Simple description of neutrinos in SU(5)

We show that experimental results for the masses and mixing of the neutrinos can be understood naturally by a simple grand unification model of SU(5) coupled to N=1 supergravity. No right-handed neutrinos are included. The left-handed neutrinos receive Majorana masses through the couplings with a Higgs boson of symmetric $\bf 15$ representation. Introducing $\bar{\bf 45}$ representation is optional for describing the masses of down-type quarks and charged leptons.

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arXiv2003

Model for neutrino mixing based on SO(10)

Assuming grand unified theory (GUT) and supersymmetry, we propose a simple model which can consistently accommodate the masses and mixings for quarks and leptons. The grand unified group is SO(10), and $\bf 10$, $\bf 120$, and $\bar {\bf 126}$ representations are introduced for the Higgs superfields which give masses to the quarks and leptons. The differences of masses and mixings between the quarks and the leptons are attributed to the Higgs boson structure. Below the GUT energy scale, the model is the same as the minimal supersymmetric standard model except its inclusion of dimension-5 operators for the small neutrino masses. The renormalization group equations of the independent parameters for the Higgs couplings with the quarks and leptons are given explicitly to connect the two energy scales of GUT and electroweak theory.

hep-ph↗
arXiv2002

Antisymmetric Higgs representation in SO(10) for neutrinos

A Model based on SO(10) grand unified theory (GUT) and supersymmetry is presented to describe observed phenomena for neutrinos. The large mixing angles among different generations, together with the small masses, are attributed to the Higgs boson structure at the GUT energy scale. Quantitative discussions for these observables are given, taking into account their energy evolution.

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arXiv2001

Large effects on $\BsBs$ mixing by vector-like quarks

We calculate the contributions of the vector-like quark model to $\BsBs$ mixing, taking into account the constraints from the decay $B\to X_sγ$. In this model the neutral bosons mediate flavor-changing interactions at the tree level. However, $\BsBs$ mixing is dominated by contributions from the box diagrams with the top quark and the extra up-type quark. In sizable ranges of the model parameters, the mixing parameter $x_s$ is much different from the standard model prediction.

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arXiv2001

Neutron Electric Dipole Moment and Extension of the Standard Model

A nonvanishing value for the electric dipole moment (EDM) of the neutron is a prominent signature for CP violation. The EDM induced by the Kobayashi-Maskawa mechanism of the standard model (SM) has a small magnitude and its detection will be very difficult. However, since baryon asymmetry of the universe cannot be accounted for by the SM, there should exist some other source of CP violation, which may generate a large magnitude for the EDM. One of the most hopeful candidates for physics beyond the SM is the supersymmetric standard model, which contains such sources of CP violation. This model suggests that the EDM has a magnitude not much smaller than the present experimental bounds. Progress in measuring the EDM provides very interesting information about extension of the SM. ........

hep-ph↗
arXiv2001

Contributions of Vector-Like Quarks to $B \to X_s γ$ and $B_s^0 \bar B_s^0$ Mixing

The radiative decay $\BSgamma$ and the mixing $\BsBs$ are discussed in the vector-like quark model which contains extra SU(2)-singlet quarks with the same electric charges as the up-type and down-type quarks. Constraints on the extended Cabibbo-Kobayashi-Maskawa matrix are obtained from the experimental results for the branching ratio of $\BSgamma$ . Within these experimental bounds, any value of the branching ratio can be accounted for by the contributions from the vector-like quarks. In sizable ranges of the model parameters, the mixing parameter for $\BsBs$ is much different from the prediction of the standard model.

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arXiv2000

New supersymmetric standard model with stable proton

We discuss a supersymmetric extension of the standard model with an extra U(1) gauge symmetry. In this model, the proton stability is guaranteed by the gauge symmetry without invoking R parity. The gauge symmetry breakdown automatically generates an effective $μ$ term and large Majorana masses for right-handed neutrinos. The supersymmetry-soft-breaking terms for scalar fields could be universal at a very high energy scale, and the electroweak symmetry is broken through radiative corrections.

hep-ph↗
arXiv2000

Contributions of vector-like quarks to radiative B meson decay

We study the decay B\to X_sγin a minimal extension of the standard model with extra up- and down-type quarks whose left- and right-handed components are both SU(2) singlets. Constraints on the extended Cabibbo-Kobayashi-Maskawa matrix are obtained from the experimental results for the branching ratio. Even if the extra quarks are too heavy to be detected in near-future colliders, the branching ratio could have a value which is non-trivially different from the prediction of the standard model.

hep-ph↗
arXiv2000

Supersymmetric Extension of the Standard Model with Naturally Stable Proton

A new supersymmetric standard model based on N=1 supergravity is constructed, aiming at natural explanation for the proton stability without invoking an ad hoc discrete symmetry through R parity. The proton is protected from decay by an extra U(1) gauge symmetry. Particle contents are necessarily increased to be free from anomalies, making it possible to incorporate the superfields for right-handed neutrinos and an SU(2)-singlet Higgs boson. The vacuum expectation value of this Higgs boson, which induces spontaneous breakdown of the U(1) symmetry, yields large Majorana masses for the right-handed neutrinos, leading to small masses for the ordinary neutrinos. The linear coupling of SU(2)-doublet Higgs superfields, which is indispensable to the superpotential of the minimal supersymmetric standard model, is replaced by a trilinear coupling of the Higgs superfields, so that there is no mass parameter in the superpotential. The energy dependencies of the model parameters are studied, showing that gauge symmetry breaking is induced by radiative corrections. Certain ranges of the parameter values compatible with phenomena at the electroweak energy scale can be derived from universal values of masses-squared and trilinear coupling constants for scalar fields at a very high energy scale.

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