arXiv subjects

Yutaka Sakamura

Publications and source records attributed to Yutaka Sakamura.

At least 55 records · Page 3Linked to original sources

arXiv2007

Anomalous Higgs Couplings in the $SO(5)\times U(1)_{B-L}$ 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 $SO(5)\times U(1)_{B-L}$ model, the couplings $WWH$ and $ZZH$ are suppressed by a factor $\cos θ_H$ from the values in the standard model, while the bare couplings $WWHH$ and $ZZHH$ are suppressed by a factor $1-(2/3)\sin^2 θ_H$. Here $θ_H$ 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 $θ_H$, contradicting with the LEP2 data.

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arXiv2007

Radius stabilization in 5D SUGRA models on orbifold

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. 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 analyse the vacuum structure of the models, especially the nature of the moduli stabilization, from the viewpoint of the effective theory.

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arXiv2007

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

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.

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arXiv2007

Effective theories of gauge-Higgs unification models in warped spacetime

We derive four-dimensional (4D) 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 $\barθ_H$ from the values in the standard model. Here $\barθ_H$ 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.

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arXiv2007

Supersymmetry breaking in a warped slice with Majorana-type masses

We study the five-dimensional (5D) supergravity compactified on an orbifold S^1/Z_2, where the U(1)_R symmetry is gauged by the graviphoton with Z_2-even coupling. In contrast to the case of gauging with Z_2-odd coupling, this class of models has Majorana-type masses and allows the Scherk-Schwarz (SS) twist even in the warped spacetime. Starting from the off-shell formulation, we show that the supersymmetry is always broken in an orbifold slice of AdS_5, irrespective of the value of the SS twist parameter. We analyze the spectra of gaugino and gravitino in such background, and find the SS twist can provide sizable effects on them in the small warping region.

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arXiv2006

WWZ, WWH, and ZZH Couplings in the Dynamical Gauge-Higgs Unification in the Warped Spacetime

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.

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arXiv2006

Scherk-Schwarz twist in 5D conformal SUGRA

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 equivalence between the SS twist and boundary constant superpotentials at the full supergravity level.

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arXiv2006

Consistent dimensional reduction of five-dimensional off-shell supergravity

There are some points to notice in the dimensional reduction of the off-shell supergravity. We discuss a consistent way of the dimensional reduction of five-dimensional off-shell supergravity compactified on S^1/Z_2. 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 the related works are also provided.

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arXiv2005

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.

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arXiv2005

Effective N=1 description of 5D conformal supergravity

We construct an effective N=1 superfield description of five-dimensional conformal supergravity. By the use of this description, we reinterpret some physical systems such as Scherk-Schwarz supersymmetry breaking from the conformal supergravity viewpoint. We also show how to introduce a radion fluctuation mode in this framework.

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arXiv2005

Dynamical Radion Superfield in Five-dimensional Action

We clarify the radion superfield dependence of 5D N=1 superspace action. The radion is treated as a dynamical field and appears in the action with the correct mode function. Our derivation is systematic and based on the superconformal formulation of 5D supergravity. We can read off the couplings of the dynamical radion superfield to the matter superfields from our result. The correct radion mass can be obtained by calculating the radion potential from our superspace action.

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arXiv2005

Dynamical radion superfield in 5D action

We derive 5D N=1 superspace action including the radion superfield. The radion is treated as a dynamical field and identified as a solution of the equation of motion even in the presence of the radius stabilization mechanism. Our derivation is systematic and based on the superconformal formulation of 5D supergravity. We can read off the couplings of the dynamical radion superfield to the matter superfields from our result. The correct radion mass can be obtained by calculating the radion potential from our superspace action.

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arXiv2004

Superfield description of 5D supergravity on general warped geometry

We provide a systematic and practical method of deriving 5D supergravity action described by 4D superfields on a general warped geometry, including a non-BPS background. Our method is based on the superconformal formulation of 5D supergravity, but is easy to handle thanks to the superfield formalism. We identify the radion superfield in the language of 5D superconformal gravity, and clarify its appearance in the action. We also discuss SUSY breaking effects induced by a deformed geometry due to the backreaction of the radius stabilizer.

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arXiv2004

Geometry mediated supersymmetry breaking

We investigate SUSY breaking mediated through the deformation of the spacetime geometry due to the backreaction of a nontrivial configuration of a bulk scalar field. To illustrate its features, we work with a toy model in which the bulk is four dimensions. Using the superconformal formulation of SUGRA, we provide a systematic method of deriving the 3D effective action expressed by the superfields.

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arXiv2004

Geometry mediated SUSY breaking

We investigate SUSY breaking mediated through the deformation of the space-time geometry due to the backreaction of a nontrivial configuration of a bulk scalar field. To illustrate its features, we work with a toy model in which the bulk is four dimensions. Using the superconformal formulation of SUGRA, we provide a systematic method of deriving the 3D effective action expressed by the superfields, which can basically be extended to 5D SUGRA straightforwardly.

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arXiv2003

CP violation in models with TeV-scale SUSY breaking

We estimate contributions of the goldstino supermultiplet to the electric dipole moment (EDM) in the case that the SUSY breaking scale Λ_S is of order the TeV scale. We found that such contributions can saturate the experimental bound if Λ_S is close to the soft mass scale. We also discuss EDM in the gaugino mediated scenario on the warped geometry as an example of models with the TeV-scale SUSY breaking.

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arXiv2003

Effective theory for wall-antiwall system

We propose a useful method for deriving the effective theory for a system where BPS and anti-BPS domain walls coexist. Our method respects an approximately preserved SUSY near each wall. Due to the finite width of the walls, SUSY breaking terms arise at tree-level, which are exponentially suppressed. A practical approximation using the BPS wall solutions is also discussed. We show that a tachyonic mode appears in the matter sector if the corresponding mode function has a broader profile than the wall width.

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arXiv2003

Superfield Description of Effective Theories on BPS Domain Walls

We derive the low-energy effective theory on the BPS domain wall in 4D N=1 global SUSY theories in terms of the 3D superfields. Our derivation makes the preserved SUSY by the wall manifest and the procedure for integrating out the massive modes easier. Our procedure clarifies how the 3D superfields are embedded into the 4D chiral and vector superfields. We also point out a shortcoming of the conventional procedure for deriving the effective theory on the wall.

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