Yutaka Sakamura

Anomalous Higgs Couplings in the SO(5) × U(1)B-L Gauge-Higgs Unification in Warped Spacetime

The gauge couplings WWZ, WWWW , and WWZZ in the gauge-Higgs unification scenario in the Randall-Sundrum warped spacetime remain almost universal as in the standard model, but substantial deviation results for the Higgs couplings. In the SO(5) × U(1)B−L model, the couplings WWH and ZZH are suppressed by a factor cos θH from the values in the standard model, while the bare couplings WWHH and ZZHH are suppressed by a factor 1− 2 3 sin θH. Here θH is the Yang-Mills AB phase (Wilson line phase) along the fifth dimension, which characterizes the electroweak symmetry breaking. The suppression can be used to test the gauge-Higgs unification scenario at LHC and ILC. It is also shown that the WWZ coupling in flat spacetime deviates from the standard model value at moderate values of θH, contradicting with the LEP2 data.

Gauge-Higgs Unification and Quark-Lepton Phenomenology in the Warped Spacetime

In the dynamical gauge-Higgs unification of electroweak interactions in the Randall-Sundrum warped spacetime, the Higgs boson mass is predicted in the range 120-290 GeV, provided that the spacetime structure is determined at the Planck scale. Couplings of quarks and leptons to gauge bosons and their Kaluza-Klein excited states are determined by the masses of quarks and leptons. All quarks and leptons other than top quarks have very small couplings to the Kaluza-Klein excited states of gauge bosons. The universality of weak interactions is slightly broken by magnitudes of 10{sup -8}, 10{sup -6}, and 10{sup -2} for {mu}-e, {tau}-e and t-e, respectively. Yukawa couplings become substantially smaller than those in the standard model, by a factor cos(1/2){theta}{sub W} where {theta}{sub W} is the non-Abelian Aharonov-Bohm phase (the Wilson line phase) associated with dynamical electroweak symmetry breaking.

Effective theories of gauge-Higgs unification models in warped spacetime

We derive four-dimensional effective theories of the gauge-Higgs unification models in the warped spacetime. The effective action can be expressed in a simple form by neglecting subleading corrections to the wave functions. We have shown in our previous works that some Higgs couplings to the other fields are suppressed by factors that depend on {theta}{sub H} from the values in the standard model. Here {theta}{sub H} is the Wilson line phase along the fifth dimension, which characterizes the electroweak symmetry breaking. The effective action derived here explicitly shows a nonlinear structure of the Higgs sector, which clarifies the origins of those suppression factors.

WWZ, WWH, and ZZH couplings in the dynamical gauge–Higgs unification in the warped spacetime

Abstract In the dynamical gauge–Higgs unification in the Randall–Sundrum warped spacetime, where the 4D Higgs field is unified with gauge fields and the electroweak symmetry is dynamically broken by the Hosotani mechanism, the trilinear couplings for WWZ , WWH , and ZZH , where H stands for the Higgs field, are evaluated. The latter two couplings are suppressed by a factor of cos θ H where θ H is the Yang–Mills Aharonov–Bohm phase in the extra dimension, while the WWZ couplings remain the same as in the standard model to good accuracy.

Roles of Z2-odd N = 1 multiplets in off-shell dimensional reduction of five-dimensional supergravity

We discuss the dimensional reduction of five-dimensional supergravity compactified on S^1/Z_2 keeping the N=1 off-shell structure. Especially we clarify the roles of the Z_2-odd N=1 multiplets in such an off-shell dimensional reduction. Their equations of motion provide constraints on the Z_2-even multiplets and extract the zero modes from the latter. The procedure can be applied to wide range of models and performed in a background-independent way. We demonstrate it in some specific models.

Scherk-Schwarz SUSY breaking from the viewpoint of 5D conformal supergravity

We reinterpret the Scherk-Schwarz (SS) boundary condition for SU(2)R in a compactified five-dimensional (5D) Poincare supergravity in terms of the twisted SU(2)U gauge fixing in 5D conformal supergravity. In such translation, only the compensator hypermultiplet is relevant to the SS twist, and various properties of the SS mechanism can be easily understood. Especially, we show the correspondence between the SS twist and constant superpotentials within our framework.

Moduli stabilization in 5D gauged supergravity with universal hypermultiplet and boundary superpotentials

Abstract We study a four-dimensional effective theory of the five-dimensional (5D) gauged supergravity with a universal hypermultiplet and perturbative superpotential terms at the orbifold fixed points. Among eight independent isometries of the scalar manifold, we focus on three directions for gauging by the graviphoton. The class of models we consider includes the 5D heterotic M-theory and the supersymmetric Randall–Sundrum model as special limits of the gauging parameters. We analyze the vacuum structure of such models, especially the nature of moduli stabilization, from the viewpoint of the effective theory. We also discuss the uplifting of supersymmetric anti-de Sitter vacua.

Consistent dimensional reduction of five-dimensional off-shell supergravity

There are some points to notice in the dimensional reduction of off-shell supergravity. We discuss a consistent way of dimensional reduction of five-dimensional off-shell supergravity compactified on

iGUT (GUT on interval)

{S}^{1}/{Z}_{2}

Scherk-Schwarz SUSY breaking from the viewpoint of 5D conformal SUGRA

. There are two approaches to the four-dimensional effective action, which are complementary to each other. Their essential difference is the treatment of the compensator and the radion superfields. We explain these approaches in detail and examine their consistency. Comments on related works are also provided.