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Yoshiharu Kawamura

Publications and source records attributed to Yoshiharu Kawamura.

At least 19 recordsLinked to original sources
arXiv2026

SU(9) grand unified model with rank-reducing discrete boundary conditions on $T^2/\mathbb Z_4$

We study a six-dimensional SU(9) grand unified model with rank-reducing discrete boundary conditions and continuous Wilson line phases on the orbifold $T^2/\mathbb Z_4$. We show that the model can realize grand unification of the Standard Model gauge interactions and electroweak symmetry breaking via the Hosotani mechanism. The model has several attractive features. Two Higgs doublets arise as zero modes of the extra-dimensional components of the gauge field, and the leptons and quarks in each generation are separately embedded into two bulk multiplets, in the ${\bf 36}$ and ${\bf 84}$ representations of SU(9), respectively, without exotic matter. Furthermore, proton decay processes mediated by the gauge bosons in the bulk are absent, because the leptons and quarks belong to different bulk multiplets.

hep-ph↗
arXiv2026

Generalized Heisenberg Dynamics Revisited

Taking as a model the fact that Heisenberg's matrix mechanics was derived from Hamiltonian mechanics using the correspondence principle, we explore a class of dynamical systems involving discrete variables, with Nambu mechanics as the starting point. Specifically, we reconstruct an extended version of matrix mechanics that describes dynamical systems possessing physical quantities expressed through generalized matrices. Furthermore, we reconfirm that a multiple commutator involving generalized matrices can serve as a discrete (quantized) version of the Nambu bracket or the Jacobian.

quant-ph↗
arXiv2025

Models with rank-reducing discrete boundary conditions on $T^2/{\mathbb Z}_4$

We study six-dimensional $SU(n)$ gauge models with rank-reducing discrete boundary conditions on the orbifold $T^2/{\mathbb Z}_4$, without and with continuous Wilson line phases. For the latter case, we find that a minimal model can describe the breakdown of the electroweak symmetry based on an $SU(6)$ gauge group. This model possesses excellent features that two Higgs doublets come from the zero modes of the extra-dimensional gauge field, and the quarks in each generation can be unified into one multiplet, without exotic quarks, as the zero modes of a bulk field in the $\boldsymbol{15}$ representation of $SU(6)$. There exists a vacuum where the electroweak symmetry is slightly broken by the Hosotani mechanism, with the addition of suitable bulk fields. %adding suitable bulk fields, and Interestingly, quadratic divergences are not reintroduced into the Higgs masses from the tadpole terms of the field strength localized on fixed points, not only at one-loop level but also at higher orders.

hep-ph↗
arXiv2025

Embedded structure in quantum theory, functional operator and multiverse

We explore a wider theoretical framework that has quantum field theory built-in, taking the fact that quantum mechanics is reconstructed from quantum field theory as a hint. We formulate a quantum theory with an embedded structure by introducing functional operators, and we find that it could describe the level II multiverse. Topics related to a beginning of the universe such as an inflation, the third quantization and the landscape are discussed in our formulation.

hep-th↗
arXiv2024

Extranatural Warped Inflation

We investigate whether inflation in the early universe can be induced by an extra component of a five-dimensional ${\rm U(1)}$ gauge field in the Randall-Sundrum warped spacetime or not. We show that an effective potential obtained by quantum corrections can act as an inflaton potential by finding parameter regions consistent with Planck 2018 results. In our model, fields involved in inflation obey a different type of boundary condition from that of the visible particles, and a surviving Wilson line phase can play a specific role for physics beyond the standard model.

hep-ph↗
arXiv2023

Flavor structure from `canonical' Yukawa interactions and `emergent' kinetic terms

We study the flavor structure of quarks in the standard model from a viewpoint of a canonical type of Yukawa interactions and an emergence of kinetic terms. A realistic structure can be generated based on the emergence proposal that quark kinetic terms appear in the infra-red region, as a result of radiative corrections involving towers of massive states.

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arXiv2023

On representation matrices of boundary conditions in $SU(n)$ gauge theories compactified on two-dimensional orbifolds

We study the existence of diagonal representatives in each equivalence class of representation matrices of boundary conditions in $SU(n)$ or $U(n)$ gauge theories compactified on the orbifolds $T^2/{\mathbb Z}_N$ ($N = 2, 3, 4, 6$). We suppose that the theory has a global $G' = U(n)$ symmetry. Using constraints, unitary transformations and gauge transformations, we examine whether the representation matrices can simultaneously become diagonal or not. We show that at least one diagonal representative necessarily exists in each equivalence class on $T^2/{\mathbb Z}_2$ and $T^2/{\mathbb Z}_3$, but the representation matrices on $T^2/{\mathbb Z}_4$ and $T^2/{\mathbb Z}_6$ can contain not only diagonal matrices but also non-diagonal $2 \times 2$ ones and non-diagonal $3 \times 3$ and $2 \times 2$ ones, respectively, as members of block-diagonal submatrices. These non-diagonal matrices have discrete parameters, which means that the rank-reducing symmetry breaking can be caused by the discrete Wilson line phases.

hep-th↗
arXiv2020

On diagonal representatives in boundary condition matrices on orbifolds

We study diagonal representatives of boundary condition matrices on the orbifolds $S^1/Z_2$ and $T^2/Z_m$ ($m=2, 3, 4, 6$). We give an alternative proof of the existence of diagonal representatives in each equivalent class of boundary condition matrices on $S^1/Z_2$, using a matrix exponential representation, and show that they do not necessarily exist on $T^2/Z_2$, $T^2/Z_3$, and $T^2/Z_4$. Each equivalence class on $T^2/Z_6$ has a diagonal representative, because its boundary conditions are determined by a single unitary matrix.

hep-th↗
arXiv2020

A bottom-up approach to fermion mass hierarchy: a case with vector-like fermions

We propose a bottom-up approach that a structure of a high-energy physics is explored by accumulating existence proofs and/or no-go theorems in the standard model or its extension. As an illustration, we study fermion mass hierarchies based on an extension of the standard model with vector-like fermions. It is shown that a magnitude of elements of Yukawa coupling matrices can become $O(1)$ and a Yukawa coupling unification can be realized in a theory beyond the extended model, if vector-like fermions mix with three families. In this case, small Yukawa couplings in the standard model can be highly sensitive to a small variation of matrix elements, and it seems that the mass hierarchy occurs as a result of a fine tuning.

hep-ph↗
arXiv2019

Chasing after flavor symmetries of quarks from bottom up

We explore a flavor structure of quarks in the standard model under the assumption that flavor symmetries exist in a theory beyond the standard model, and chase after their properties, using a bottom-up approach. We reacknowledge that a flavor-symmetric part of Yukawa coupling matrix can be realized by a rank-one matrix and a democratic-type one occupies a special position, based on Dirac's naturalness.

hep-ph↗
arXiv2019

Yukawa interactions, flavor symmetry, and non-canonical Kähler potential

We study the origin of fermion mass hierarchy and flavor mixing in the standard model, paying attention to flavor symmetries and fermion kinetic terms. There is a possibility that the hierarchical flavor structure of quarks and charged leptons originates from non-canonical types of fermion kinetic terms in the presence of flavor symmetric Yukawa interactions. A flavor symmetry can be hidden in the form of non-unitary bases in the standard model. The structure of Kähler potential can become a touchstone of new physics.

hep-ph↗
arXiv2018

Orbifold family unification using vectorlike representation on six dimensions

In orbifold family unification on the basis of $SU(N)$ gauge theory on the six-dimensional space-time $M^4\times T^2/Z_m$ ($m=2, 3, 4, 6$), enormous numbers of models with three families of the standard model matter multiplets are derived from a massless Dirac fermion with a vectorlike representation $[N, 3] + [N, N-3]$ of $SU(N)$ ($N = 8, 9$). They contain models with three or more than three neutrino singlets and without any non-Abelian continuous flavor gauge symmetries. The relationship between flavor numbers from a fermion with $[N, N-k]$ and those from a fermion with $[N, k]$ are studied from the viewpoint of charge conjugation.

hep-ph↗
arXiv2018

Left-right symmetry, orbifold $S^1/Z_2$, and radiative breaking of $U(1)_{\rm R} \times U(1)_{\rm B-L}$

We study the origin of electroweak symmetry under the assumption that $SU(4)_{\rm C} \times SU(2)_{\rm L} \times SU(2)_{\rm R}$ is realized on a five-dimensional space-time. The Pati-Salam type gauge symmetry is reduced to $SU(3)_{\rm C} \times SU(2)_{\rm L} \times U(1)_{\rm R} \times U(1)_{\rm B-L}$ by orbifold breaking mechanism on the orbifold $S^1/Z_2$. The breakdown of residual gauge symmetries occurs radiatively via the Coleman-Weinberg mechanism, such that the $U(1)_{\rm R} \times U(1)_{\rm B-L}$ symmetry is broken down to $U(1)_{\rm Y}$ by the vacuum expectation value of an $SU(2)_{\rm L}$ singlet scalar field and the $SU(2)_{\rm L} \times U(1)_{\rm Y}$ symmetry is broken down to the electric one $U(1)_{\rm EM}$ by the vacuum expectation value of an $SU(2)_{\rm L}$ doublet scalar field regarded as the Higgs doublet. The negative Higgs squared mass term is originated from an interaction between the Higgs doublet and an $SU(2)_{\rm L}$ singlet scalar field as a Higgs portal. The vacuum stability is recovered due to the contributions from Kaluza-Klein modes of gauge bosons.

hep-ph↗
arXiv2017

Dark energy from gravitational corrections

We study physics concerning the cosmological constant problem in the framework of effective field theory and suggest that a dominant part of dark energy can originate from gravitational corrections of vacuum energy, under the assumption that the classical gravitational fields do not couple to a large portion of the vacuum energy effectively, in spite of the coupling between graviton and matters at a microscopic level. Our speculation is excellent with terascale supersymmetry.

hep-th↗
arXiv2016

Conjugate boundary condition, hidden particles, and gauge-Higgs inflation

We propose an idea that hidden particles can be separated according to gauge quantum numbers from the visible ones by the difference of boundary conditions on extra dimensions. We formulate 5-dimensional gauge theories yielding conjugate boundary conditions besides ordinary ones on $S^1/Z_2$, and examine physical implications concerning hidden particles on an extension of the standard model coexisting different types of boundary conditions. A model with conjugate boundary conditions is applied on a gauge-Higgs inflation scenario.

hep-ph↗
arXiv2015

Predictions of $SU(9)$ orbifold family unification

We study predictions of orbifold family unification models with $SU(9)$ gauge group on a six-dimensional space-time including the orbifold $T^2/Z_2$, and obtain relations among sfermion masses in the supersymmetric extension of models. The models have an excellent feature that just three families of the standard model fermions exist in a pair of Weyl fermions in the $[9, 3]$ representation as four-dimensional zero modes, without accompanying any mirror particles.

hep-ph↗
arXiv2015

Release of physical modes from unphysical fields

We present a basic idea and a toy model that physical modes originate from unobservable fields. The model is defined on a higher-dimensional space-time and has fermionic symmetries that make fields unphysical, and observable modes can appear through a dimensional reduction.

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