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Nobuhiro Uekusa

Publications and source records attributed to Nobuhiro Uekusa.

At least 19 recordsLinked to original sources
arXiv2011

Collider signatures of the SO(5) x U(1) gauge-Higgs unification

Collider signatures of the $SO(5) \times U(1)$ gauge-Higgs unification model in the Randall-Sundrum warped space are explored. Gauge couplings of quarks and leptons receive small corrections from the fifth dimension whose effects are tested by the precision data. It is found that the forward-backward asymmetries in $e^+e^-$ collisions on the $Z$ pole are well explained in a wide range of the warp factor $z_L$, but the model is consistent with the branching fractions of $Z$ decay only for large $z_L \simg 10^{15}$. Kaluza-Klein (KK) spectra of gauge bosons, quarks, and leptons as well as gauge and Higgs couplings of low-lying KK excited states are determined. Right-handed quarks and leptons have larger couplings to the KK gauge bosons than left-handed ones. Production rates of Higgs bosons and KK states at Tevatron, LHC and ILC are evaluated. The first KK $Z$ has a mass 1130 GeV with a width 422 GeV for $z_L = 10^{15}$. The current limit on the $Z'$ production at Tevatron and LHC indicates $z_L >10^{15}$. A large effect of parity violation appears in the difference between the rapidity distributions of $e^+$ and $e^-$ in the decay of the first KK $Z$. The first KK gauge bosons decay into light and heavy quarks evenly.

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arXiv2011

Most attractive channel for self-breaking of grand unification group symmetry

Most attractive channel is studied for SU(5) grand unified theory in five dimensions where 5* and 10 fermions and a 24 gauge boson propagate in the bulk. If there are bulk fermions with zero mode for the chirality opposite to quark and lepton multiplets, they can contribute to forming 5, 24, 50 and 75 scalar bound states. We find that the inclusion of a simple anomaly-free set for zero mode yields scalar bound states whose binding strengths are the largest for 24 and the second largest for 5. This corresponds to the breaking pattern of the SU(5) to color and electromagnetism via the standard model gauge group.

hep-ph↗
arXiv2011

Most-attractive-channel study for bulk and brane fermions in warped space

The idea of the self-breaking of the standard model gauge symmetry is applied to a gauge theory in a warped space. We systematically examine the gauge couplings of bulk and brane fermions. The constraint on the masses of bulk fermions is found under the conditions that the ordinary four-dimensional massless gluon is not condensed and that color-triplet scalar bound states are not formed. For bulk fermions with zero modes for the left- and right-handed components, the mass parameters are required to be at least $c\simg 1/2$ and $c\siml -1/2$, respectively. Then possible vacuum expectation values arise only from weak-doublet scalar bound states which trigger electroweak symmetry breaking.

hep-ph↗
arXiv2010

H parity and the stable Higgs boson in the SO(5) x U(1) gauge-Higgs unification

In the SO(5) x U(1) gauge-Higgs unification model in the Randall-Sundrum warped space there results the conservation of the H parity. The H parity is assigned to all 4D fields including excited modes in Kaluza-Klein towers. The neutral Higgs boson is the lightest particle of odd H parity, consequently becoming absolutely stable. Its mass is found to be 70 \sim 135 GeV for the warp factor z_L = 10^5 \sim 10^{15}.

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arXiv2010

Marginal operators in quantum field theory with extra dimensions

The classification of relevant, marginal and irrelevant operators is studied in the Randall-Sundrum spacetime. We find that there exist marginal and interacting operators in the Randall-Sundrum spacetime unlike a higher-dimensional effective theory near the free-field fixed point. This gives a direction to treat quantum corrections in the field-theoretical framework with extra dimensions by constructing models out of relevant and marginal operators.

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arXiv2010

Low energy kinetic distribution on orbifolds

Fermion self-energy associated with wave function renormalization is studied in a five-dimensional Yukawa theory on the orbifold S1/Z2. One-loop divergence can be subtracted with only two renormalization constants in the bulk and on the branes. We show that the bulk and brane parts of the self-energy are uniquely determined with requiring physical conditions. With this procedure, momentum-scale dependence of the renormalized self-energy is given and the distribution of the bulk and brane parts can be found at low and high energies. Despite possible higher degrees of divergence in higher dimensions, the regularization scheme dependence does not arise. A viewpoint of the regularization scheme dependence at higher-loop level is also discussed. We find that the ratio of the bulk contribution to the brane contribution depends on the momentum scale in a very mild way, so that the relative coefficient of bulk and brane kinetic terms can be regarded as approximately constant for the leading quantum effect. The physical conditions given here are applicable to remove ambiguity in various orbifold models.

hep-ph↗
arXiv2010

Intermediate-scale vertex corrections for zero mode in warped space

Non-Abelian gauge theory with a warped extra dimension is studied as a quantum field theory at an intermediate scale that is regarded as being much lower than the scale of the geometry stabilization and the Planck scale. Loop corrections for zero-mode vertices are diagrammatically calculable in perturbation at the intermediate scale. The contribution for each diagram can be compared to the correspondent in the four-dimensional theory. It is found that for a part of the contributions the coefficient for the logarithmic scaling has the same value as the four-dimensional results. A viewpoint to treat corrections associated with higher-dimensional operators is also discussed.

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arXiv2010

Forward-backward asymmetry on Z resonance in SO(5) x U(1) gauge-Higgs unification

We find that the tree-level predictions of the forward-backward production asymmetries on the Z resonance for b and c quarks, A_FB, in an SO(5) x U(1) gauge-Higgs unification model are markedly close to the central values of the Particle Data Group data unlike the standard model. The decay width of Z boson is evaluated and the S and T parameters are discussed.

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arXiv2010

Asymptotic behavior of Lorentz violation on orbifolds

Momentum dependence of quantum corrections with higher-dimensional Lorentz violation is examined in electrodynamics on orbifolds. It is shown that effects of the Lorentz violation are not decoupled at high energy scales. Despite the loss of the higher-dimensional Lorentz invariance, a higher-dimensional Ward identity is found to be fulfilled for one-loop vacuum polarization. This implies that gauge invariance may be prior to Lorentz invariance as a guiding principle in higher-dimensional field theory. As a universal application of electrodynamics, an extra-dimensional aspect for Furry's theorem is emphasized.

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arXiv2010

Total-derivative supersymmetry breaking

On an interval compactification in supersymmetric theory, boundary conditions for bulk fields must be treated carefully. If they are taken arbitrarily following the requirement that a theory is supersymmetric, the conditions could give redundant constraints on the theory. We construct a supersymmetric action integral on an interval by introducing brane interactions with which total derivative terms under the supersymmetry transformation become zero due to a cancellation. The variational principle leads equations of motion and also boundary conditions for bulk fields, which determine boundary values of bulk fields. By estimating mass spectrum, {\it spontaneous} supersymmetry breaking in this simple setup can be realized in a new framework. This supersymmetry breaking does not induce massless R-axion, which is favorable for phenomenology. It is worth noting that fermions in hyper-multiplet, gauge bosons, and the fifth-dimensional component of gauge bosons can have zero-modes (while the other components are all massive as Kaluza-Klein modes), which fits the gauge-Higgs unification scenarios.

hep-ph↗
arXiv2010

The electroweak gauge couplings in SO(5) x U(1) gauge-Higgs unification

The electroweak currents of quarks and leptons in the $SO(5) \times U(1)$ gauge-Higgs unification model in the Randall-Sundrum warped space are determined. The 4D gauge couplings deviate from those in the standard model and the weak universality is slightly violated. It is shown that the model is free from 4D anomalies and the deviations of the gauge couplings are tiny, less than 1% except for the top quark. The $Zt_L \bar t_L$, $Zt_R \bar t_R$, $Zb_L \bar b_L$ and $Zb_R \bar b_R$ couplings deviate from those in the standard model by -7%, 18%, 0.3% and 0.9% with the warp factor $z_L = 10^{15}$, respectively. The violation of the $μ$-$e$, $τ$-$e$ and $t$-$e$ universality in the charged current interactions is ${\cal O}(10^{-8})$, ${\cal O}(10^{-6})$ and 2.3%, respectively.

hep-ph↗
arXiv2010

Simple mass relations for bulk fermions

Relations between bulk mass parameters for fermions propagating in higher dimensions are studied in analogy with the empirical mass relation for charged leptons. Masses of three generation of four-dimensional charged leptons are achieved from the bulk mass parameters of the same-order values. We find that the observed pattern of charged lepton mass spectrum is accommodated approximately in a set of simple relations for bulk and physical masses.

hep-ph↗
arXiv2009

Two-loop corrections and predictability on orbifold

We study quantum loop corrections to two-point functions and extraction of physical quantities in a five-dimensional $ϕ^4$ theory on an orbifold. At two-loop level, we find that divergence for quartic derivative terms of $(p^2)^2$ appear as Lagrangian terms in the bulk. The counterterms are needed and these terms make propagators have two poles. With this effect taken into account, corrections to masses are derived. We show that for extraction of physical quantities for two-point functions an ultraviolet cutoff must be orders of magnitude larger compared to a compactification scale. Even higher derivative corrections at higher loop levels are also discussed.

hep-ph↗
arXiv2009

Mass ratio of W and Z bosons in SU(5) gauge-Higgs unification

We study the mass ratio of W and Z bosons in an SU(5) gauge-Higgs unification model with the left-right symmetry remaining locally for boundary conditions and with no scalar fields except for the extra-dimensional component of gauge bosons. We find that there are a variety of boundary conditions to yield distinct values of the mass ratio.

hep-ph↗
arXiv2009

Operators in ultraviolet completions for collective symmetry breaking

We investigate the Lagrangian terms of scalar-gauge interactions in a weakly-coupled gauge theory beyond the ultraviolet momentum cutoff of models where the collective symmetry breaking mechanism protects the Higgs mass squared against having quadratic divergence. We also propose a five-dimensional model in which the gauge symmetry breaking is achieved by boundary conditions consistent with local gauge transformations. It is shown that the scalar-gauge operators in the two models differ in the absence of quadratic divergence.

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arXiv2008

The lightest Higgs boson mass in effective field theory with bulk and brane supersymmetry breaking

We study the mass of the lightest Higgs boson in an effective Kaluza-Klein theory with two sources of supersymmetry breaking. When stop mass matrices are non-diagonal with respect to Kaluza-Klein modes and each element is not small in unit of the inverse compactification radius, a very small eigenvalue can be accommodated in the diagonalized basis. We show that in the model with the two sources, the Higgs boson mass can receive suitable corrections for various compactification radii.

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arXiv2008

Anomaly Mediation and Radius Stabilization by a Boundary Constant Superpotential in a Warped Space

We present a very simple model of the radius stabilization in a supersymmetric (SUSY) Randall-Sundrum model with a hypermultiplet and a boundary constant superpotential. A wide range of parameters where the anomaly mediation of SUSY breaking is dominated is found although there are many problematic bulk effects of SUSY breaking. A negative cosmological constant in the radius stabilized vacuum can be cancelled by a localized SUSY breaking. Making use of this localized SUSY breaking also solves the μ-problem by Giudice-Masiero mechanism.

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