arXiv subjects

Yutaka Hosotani

Publications and source records attributed to Yutaka Hosotani.

At least 19 recordsLinked to original sources

arXiv2026

Anomaly flow and anomaly cancellation

In gauge theory on 5D orbifolds the magnitude of chiral anomalies of 4D gauge fields changes with the value of the Aharonov-Bohm (AB) phase $θ_H$ in the fifth dimension. Anomaly flows with the AB phase. In particular in the Randall-Sundrum (RS) warped space gauge couplings of 4D fermions depend on bulk mass parameters of 5D fermion multiplets. We show that in the GUT-inspired $SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification model in the RS warped space the total anomalies including contributions of all Kaluza-Klein excited modes of fermions become universal, being independent of the values of the bulk mass parameters of fermions and expressed in terms of the values of $W$ and $Z$ wave functions at the ultraviolet and infrared branes in the RS space. It is shown that cancellation of gauge anomalies is achieved in each generation even for $θ_H \not= 0$.

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arXiv2026

Neutrino oscillations and PMNS matrix in gauge-Higgs unification

In the $SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification in the Randall-Sundrum (RS) warped space neutrino oscillations and the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix in the $W$ couplings originate from Majorana mass terms on the ultraviolet brane in the RS space. Tiny neutrino masses are generated by an inverse seesaw mechanism. The PMNS matrix in the normal ordering with $δ_{CP}=π$ naturally arises consistently with the NuFit-6.0 analysis of neutrino oscillation data.

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arXiv2025

Origin of CKM matrix and natural FCNC suppression in gauge-Higgs unification

In the $SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification in the Randall-Sundrum warped space the mixing in the $W$ couplings in the quark sector is induced by masses of $SO(5)$ singlet fermions which are responsible for splitting masses of down-type quarks from those of up-type quarks in each generation. We show that the observed Cabibbo-Kobayashi-Maskawa (CKM) matrix in the $W$ couplings is reproduced within experimental errors. Further flavor-changing neutral currents (FCNCs) in the quark sector are shown to be naturally suppressed.

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arXiv2024

Coupling Sum Rules and Oblique Corrections in Gauge-Higgs Unification

In GUT inspired $SO(5) \times U(1)_X \times SU(3)_C$ gauge-Higgs unification (GHU) in the Randall-Sundrum warped spacetime, the $W$ and $Z$ couplings of all 4D fermion modes become nontrivial. The $W$ and $Z$ couplings of zero-mode quarks and leptons slightly deviate from those in the SM, and the couplings take the matrix form in the space of Kaluza-Klein (KK) states. In particular, the 4D couplings and mass spectra in the KK states depend on the Aharonov-Bohm phase $ θ_H$ in the fifth dimension. Nevertheless there emerge three astonishing sum rules among those coupling matrices, which guarantees the finiteness of certain combinations of corrections to vacuum polarization tensors. We confirm by numerical evaluation that the equality in the sum rules holds with 5 to 7 digits accuracy. Based on the sum rules we propose improved oblique parameters in GHU. Oblique corrections due to fermion 1-loop diagrams are found to be small.

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arXiv2023

$W$ boson mass in gauge-Higgs unification

The $W$ boson mass $m_W$ in the GUT inspired $SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification in the Randall-Sundrum (RS) warped space is evaluated. The muon decay $μ^- \rightarrow e^- \barν_e ν_μ$ proceeds by the exchange of not only the zero mode of the $W$ boson $(W^{(0)}$) but also Kaluza-Klein (KK) excited modes $W^{(n)}$ and $W_R^{(n)}$ ($n \ge 1$) at the tree level. The anti-de Sitter curvature of the RS space also affects the relationship among the gauge couplings and the ratio of $m_W$ to the $Z$ boson mass $m_Z$. The $W$ couplings of leptons and quarks also change. With the given KK mass scale $m_{\rm KK}$ the range of the Aharonov-Bohm phase $θ_H$ in the fifth dimension is constrained. For $m_{\rm KK} = 13\,$TeV, $0.085 \lesssim θ_H \lesssim 0.11$ and $80.381\,{\rm GeV} \lesssim m_W \lesssim 80.407\,{\rm GeV}$. The predicted value of $m_W$ for $13\, {\rm TeV} \le m_{\rm KK} \le 20\, {\rm TeV}$ lies between $m_W^{\rm SM} = 80.354 \pm 0.007\,$GeV in the standard model and $m_W^{\rm CDF} = 80.4335 \pm 0.0094\,$GeV, the value reported by the CDF collaboration in 2022.

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arXiv2023

$W$ and $Z$ Boson Pair Production at Electron-Positron Colliders in Gauge-Higgs Unification

We examine $W$ and $Z$ boson pair production processes at electron-positron collider experiments in the $SU(3)_C\times SO(5)_W\times U(1)_X$ gauge-Higgs unification (GHU) model. We find that the deviation of the total cross section for the $e^-e^+\to W^-W^+$ process from the Standard Model (SM) in the GHU model with parameter sets, which are consistent with the current experiments, is about 0.5% to 1.5% and 0.6% to 2.2% for $\sqrt{s}=250$GeV and 500GeV, respectively, depending on the initial electron and positron polarization. We find that for the $e^-e^+\to ZZ$ process the deviation from the SM in the GHU model is at most 1%. We find that unitality bound for the $e^-e^+\to W^-W^+$ process is satisfied in the GHU model as in the SM, as a consequence of the relationship among coupling constants.

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arXiv2023

Holography in anomaly flow in orbifold gauge theory

In orbifold gauge theory and gauge-Higgs unification models, gauge anomaly flows with an Aharonov-Bohm phase $θ_H$ in the fifth dimension. We analyze $SU(2)$ gauge theory with doublet fermions in the flat $M^4 \times (S^1/Z_2)$ spacetime and in the Randall-Sundrum (RS) warped space. With orbifold boundary conditions the $U(1)$ part of gauge symmetry remains unbroken at $θ_H = 0$ and $π$. Chiral anomalies smoothly vary with $θ_H$ in the RS space. Anomaly coefficients associated with this anomaly flow are expressed in terms of the values of the wave functions of gauge fields at the UV and IR branes in the RS space and parity conditions of fermion fields. Holography in anomaly flow is observed. Conditions for the anomaly cancellation turn out independent of $θ_H$.

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arXiv2022

Probing the minimal $U(1)_X$ model at future electron-positron colliders via the fermion pair-production channel

The minimal $U(1)_X$ extension of the Standard Model (SM) is a well-motivated new physics scenario, where anomaly cancellation dictates new neutral gauge boson ($Z^\prime$) couplings with the SM fermions in terms of the $U(1)_X$ charges of the new scalar fields. We investigate the SM charged fermion pair-production process for different values of these $U(1)_X$ charges at future $e^-e^+$ colliders: $e^+e^-\to f\bar f$. Apart from the standard $γ$ and $Z$-mediated processes, this model features additional $s$-channel (or both $s$ and $t$-channel when $f=e^-$) $Z^\prime$ exchange which interferes with the SM processes. We first estimate the bounds on the $U(1)_X$ coupling $(g^\prime)$ and the $Z^\prime$ mass $(M_{Z^\prime})$ considering the latest dilepton and dijet constraints from the heavy resonance searches at the LHC. Then using the allowed values of $g^\prime$, we study the angular distributions, forward-backward $(\mathcal{A}_{\rm{FB}})$, left-right $(\mathcal{A}_{\rm{LR}})$ and left-right forward-backward $(\mathcal{A}_{\rm{LR, FB}})$ asymmetries of the $f\bar{f}$ final states. We find that these observables can show substantial deviations from the SM results in the $U(1)_X$ model, thus providing a powerful probe of the multi-TeV $Z^\prime$ bosons at future $e^+e^-$ colliders.

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arXiv2022

Bhabha scattering in the gauge-Higgs unification

We examine effects of $Z'$ bosons in gauge-Higgs unification (GHU) models at $\mathrm{e}^{+}\mathrm{e}^{-}\to \mathrm{e}^{+}\mathrm{e}^{-}$ Bhabha scatterings. We evaluate differential cross sections in Bhabha scatterings including $Z'$ bosons in two types of $\mathrm{SO}(5) \times \mathrm{U}(1) \times \mathrm{SU}(3)$ GHU models. We find that deviations of differential cross sections in the GHU models from those in the SM can be seen at $\sqrt{s} = 250\,\mathrm{GeV}$. With $80\%$-longitudinally polarized electron and $30\%$-longitudinally polarized positron beams, the left-right asymmetries in the GHU A- and B-models are resolved at more than $3\,σ$ at $L_{\rm int} =250\,\mathrm{fb}^{-1}$. We also show that Bhabha scattering with scattering angle less than 100 mrad can be safely used as luminosity measurements in $\mathrm{e}^{+}\mathrm{e}^{-}$ colliders since the effects of $Z'$ bosons are well suppressed for small scattering angle. We propose a new observable which can be measured at future TeV-scale $\mathrm{e}^{+} \mathrm{e}^{-}$ linear colliders.

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arXiv2022

Universality in Anomaly Flow

Universality in anomaly flow by an Aharonov-Bohm (AB) phase $θ_H$ is shown in the flat $M^4 \times (S^1/Z_2)$ spacetime and in the Randall-Sundrum (RS) warped space. We analyze $SU(2)$ gauge theory with doublet fermions. With orbifold boundary conditions the $U(1)$ part of gauge symmetry remains unbroken at $θ_H = 0$ and $π$. Chiral anomalies smoothly vary with $θ_H$ in the RS space. It is shown that anomaly coefficients associated with this anomaly flow are expressed in terms of the values of the wave functions of gauge fields at the UV and IR branes in the RS space. The anomaly coefficients depend on $θ_H$, the warp factor of the RS space, and the orbifold boundary conditions for fermions, but not on the bulk mass parameters of fermions.

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arXiv2022

Signals of $W'$ and $Z'$ bosons at the LHC in the $SU(3) \times SO(5) \times U(1)$ gauge-Higgs unification

The $pp\to \{W, W'\} \to lν$ and $pp\to \{γ, Z, Z'\} \to l^+l^-$ ($l=e,μ$) processes in the $SU(3)_C\times SO(5)\times U(1)_X$ gauge-Higgs unification (GHU) models are studied, where $W'$ and $Z'$ bosons are Kaluza-Klein (KK) exited states of the electroweak gauge bosons. From the experimental data collected at the Large Hadron Collider, constraints on the KK mass scale and the Aharonov-Bohm phase are obtained. One can explore the KK mass scale in the GUT inspired GHU model up to 18 TeV for the luminosity 300 fb$^{-1}$ and 22 TeV for the luminosity 3000 fb$^{-1}$ at $\sqrt{s}=14$ TeV.

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arXiv2022

Anomaly flow by an Aharonov-Bohm phase

In gauge-Higgs unification (GHU), gauge symmetry is dynamically broken by an Aharonov-Bohm (AB) phase, $θ_H$, in the fifth dimension. We analyze $SU(2)$ GHU with an $SU(2)$ doublet fermion in flat $M^4 \times (S^1/Z_2)$ spacetime and in the Randall-Sundrum (RS) warped space. With orbifold boundary conditions the $U(1)$ part of gauge symmetry remains unbroken at $θ_H = 0$ and $π$. The fermion multiplet has chiral zero modes at $θ_H = 0$, which become massive at $θ_H = π$. In other words chiral fermions are transformed to vectorlike fermions by the AB phase $θ_H$. Chiral anomaly at $θ_H = 0$ continuously varies as $θ_H$ and vanishes at $θ_H=π$. We demonstrate this intriguing phenomenon in the RS space in which there occurs no level crossing in the mass spectrum and everything varies smoothly. The flat spacetime limit is singular as the AdS curvature of the RS space diminishes, and reproduces the result in the flat spacetime. Anomalies appear for various combinations of Kaluza-Klein excitation modes of gauge fields as well. Although the magnitude of anomalies depends on $θ_{H}$ and the warp factor of the RS space, it does not depend on the bulk mass parameter of the fermion field controlling its mass and wave function at general $θ_H$.

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arXiv2021

Electroweak and Left-Right Phase Transitions in $SO(5) \times U(1) \times SU(3)$ Gauge-Higgs Unification

The electroweak phase transition in GUT inspired $SO(5)\times U(1) \times SU(3)$ gauge-Higgs unification is shown to be weakly first order and occurs at $T = T_c^{\rm EW} \sim 163\,$GeV, which is very similar to the behavior in the standard model in perturbation theory. A new phase appears at higher temperatures. $SU(2)_L \times U(1)_Y$ ($θ_H=0$) and $SU(2)_R \times U(1)_{Y'}$ ($θ_H=π$) phases become almost degenerate above $T \sim m_{\rm KK}$ where $m_{\rm KK}$ is the Kaluza-Klein mass scale typically around 13$\,$TeV and $θ_H$ is the Aharonov-Bohm phase along the fifth dimension. The two phases become degenerate at $T = T_c^{\rm LR} \sim m_{\rm KK}$. As the temperature drops in the evolution of the early Universe the $SU(2)_R \times U(1)_{Y'}$ phase becomes unstable. The tunneling rate from the $SU(2)_R \times U(1)_{Y'}$ phase to the $SU(2)_L \times U(1)_Y$ phase becomes sizable and a first-order phase transition takes place at $T=2.5 \sim 2.6\,$TeV. The amount of gravitational waves produced in this left-right phase transition is small, far below the reach of the sensitivity of Laser Interferometer Space Antenna (LISA). A detailed analysis of the $SU(2)_R \times U(1)_{Y'}$ phase is also given. It is shown that the $W$ boson, $Z$ boson and photon, with $θ_H$ varying from 0 to $π$, are transformed to gauge bosons in the $SU(2)_R \times U(1)_{Y'}$ phase. Gauge couplings and wave functions of quarks, leptons and dark fermions in the $SU(2)_R \times U(1)_{Y'}$ phase are determined.

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arXiv2021

Linear Collider Signals of $Z'$ Bosons in GUT Inspired Gauge-Higgs Unification

In gauge-Higgs unification (GHU), the 4D Higgs boson appears as a part of the fifth dimensional component of 5D gauge field. Recently, an $SO(11)$ GUT inspired $SO(5)\times U(1)\times SU(3)$ GHU model has been proposed. In the GHU, Kaluza-Klein (KK) excited states of neutral vector bosons, photon, $Z$ boson and $Z_R$ boson, appear as neutral massive vector bosons $Z'$s. The $Z'$ bosons in the GHU couple to quarks and leptons with large parity violation, which leads to distinctive polarization dependence in, e.g., cross sections and forward-backward asymmetries in $e^-e^+\toμ^-μ^+,q\bar{q}$ processes. In the talk, we discuss fermion pair production in $e^-e^+$ linear collider experiments with polarized $e^-$ and $e^+$ beams in the GUT inspired GHU. Deviations from the SM are shown in the early stage of planned international linear collider (ILC) with 250 GeV experiments. The deviations can be tested for the KK mass scale up to about 15 TeV. This talk is mainly based on Phys.Rev.D102(2020)015029.

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arXiv2020

Fermion pair production at $e^- e^+$ linear collider experiments in GUT inspired gauge-Higgs unification

Fermion pair production at $e^-e^+$ linear collider experiments with polarized $e^-$ and $e^+$ beams is examined in the GUT inspired $SO(5)\times U(1)\times SU(3)$ gauge-Higgs unification. There arises large parity violation in the couplings of leptons and quarks to Kaluza-Klein (KK) excited neutral vector bosons $Z'$s, which leads to distinctive polarization dependence in cross sections, forward-backward asymmetries, left-right asymmetries, and left-right forward-backward asymmetries in various processes. Those effects are detectable even for the KK mass scale up to about 15 TeV at future $e^-e^+$ linear collider experiments with energies 250$\,$GeV to 1$\,$TeV.

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arXiv2020

The effective potential and universality in GUT inspired gauge-Higgs unification

The effective potential for the Aharonov-Bohm phase $θ_H$ in the fifth dimension in GUT inspired $SO(5)\times U(1) \times SU(3)$ gauge-Higgs unification is evaluated to show that dynamical electroweak symmetry breaking takes place with $θ_H \not= 0$, the 4D Higgs boson mass 125$\,$GeV being generated at the quantum level. The cubic and quartic self-couplings $(λ_3, λ_4)$ of the Higgs boson are found to satisfy universal relations, i.e. they are determined, to high accuracy, solely by $θ_H$, irrespective of values of other parameters in the model. For $θ_H=0.1$ ($0.15$), $λ_3$ and $λ_4$ are smaller than those in the standard model by 7.7% (8.1%) and 30% (32%), respectively.

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arXiv2020

CKM matrix and FCNC suppression in $SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification

The Cabibbo-Kobayashi-Maskawa (CKM) mixing matrix and flavor-changing neutral currents (FCNC's) in the quark sector are examined in the GUT inspired $SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification in which the 4D Higgs boson is identified with the Aharonov-Bohm phase in the fifth dimension. Gauge invariant brane interactions play an important role for the flavor mixing in the charged-current weak interactions. The CKM matrix is reproduced except that the up quark mass needs to be larger than the observed one. FCNC's are naturally suppressed as a consequence of the gauge invariance, with a factor of order $10^{-6}$. It is also shown that induced flavor-changing Yukawa couplings are extremely small.

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arXiv2019

GUT inspired $SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification

$SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification model inspired by $SO(11)$ gauge-Higgs grand unification is constructed in the Randall-Sundrum warped space. The 4D Higgs boson is identified with the Aharonov-Bohm phase in the fifth dimension. Fermion multiplets are introduced in the bulk in the spinor, vector and singlet representations of $SO(5)$ such that they are implemented in the spinor and vector representations of $SO(11)$. The mass spectrum of quarks and leptons in three generations is reproduced except for the down quark mass. The small neutrino masses are explained by the gauge-Higgs seesaw mechanism which takes the same form as in the inverse seesaw mechanism in grand unified theories in four dimensions.

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