arXiv subjects

K. Takenaga

Publications and source records attributed to K. Takenaga.

At least 19 recordsLinked to original sources

arXiv2013

The Standard Model with New Order Parameters at Finite Temperature

We consider the finite temperature effective potential of the standard model at the one-loop level in four dimensions by taking account of two kinds of order parameters, the Higgs vacuum expectation value and the zero modes of gauge fields for the Euclidean time direction. We study the vacuum structure of the model, focusing on the existence of new phase, where the zero modes, that is, the new order parameters develop nontrivial vacuum expectation values except for the center of the gauge group. We find that under certain conditions there appears no new phase at finite temperature.

hep-th↗

arXiv2010

Symmetry and Z_2-Orbifolding Approach in Five-dimensional Lattice Gauge Theory

In a lattice gauge-Higgs unification scenario using a Z_2-orbifolded extra-dimension, we find a new global symmetry in a case of SU(2) bulk gauge symmetry. It is a global symmetry on sites in a fixed point with respect to Z_2-orbifolding, independent of the bulk gauge symmetry. It is shown that the vacuum expectation value of a Z_2-projected Polyakov loop is a good order parameter of the new symmetry. The effective theory on lattice is also discussed.

hep-lat↗

arXiv2007

On Gauge Symmetry Breaking via Euclidean Time Component of Gauge Fields

We study gauge theories with/without an extra dimension at finite temperature, in which there are two kinds of order parameters of gauge symmetry breaking. The one is the zero mode of the gauge field for the Euclidean time direction and the other is that for the direction of the extra dimension. We evaluate the effective potential for the zero modes in one-loop approximation and investigate the vacuum configuration in detail. Our analyses show that gauge symmetry can be broken only through the zero mode for the direction of the extra dimension and no nontrivial vacuum configuration of the zero mode for the Euclidean time direction is found.

hep-th↗

arXiv2007

Two loop finiteness of Higgs mass and potential in the gauge-Higgs unification

The zero mode of an extra-dimensional component of gauge potentials serves as a 4D Higgs field in the gauge-Higgs unification. We examine QED on $M^4 \times S^1$ and determine the mass and potential of a 4D Higgs field (the $A_5$ component) at the two loop level with gauge invariant reguralization. It is seen that the mass is free from divergences and independent of the renormalization scheme.

hep-ph↗

arXiv2001

Dynamics of Nonintegrable Phases in Softly Broken Supersymmetric Gauge Theory with Massless Adjoint Matter

We study SU(N) supersymmetric Yang-Mills theory with massless adjoint matter defined on $M^3\otimes S^1$. The SU(N) gauge symmetry is broken maximally to $U(1)^{N-1}$, independent of the number of flavor and the boundary conditions of the fields associated with the Scherk-Schwarz mechanism of supersymmetry breaking. The mass of the Higgs scalar is generated through quantum corrections in the extra dimensions. The quantum correction can become manifest by a finite Higgs boson mass at low energies even in the limit of small extra dimensions thanks to the supersymmetry breaking parameter of the Scherk-Schwarz mechanism.

hep-th↗

arXiv2000

SUSY Breaking through Compactification

We propose a new mechanism of spontaneous supersymmetry breaking. The existence of extra dimensions with nontrivial topology plays an important role. We investigate new features resulting from this mechanism. One noteworthy feature is that there exists a phase in which the translational invariance for the compactified directions is broken spontaneously. The mechanism we propose also yields quite different vacuum structures for models with different global symmetries.

hep-th↗

arXiv2000

Quantization Ambiguity and Supersymmetric Ground State Wave Functions

Supersymmetric ground state wave functions of a model of supersymmetric quantum mechanics on $S^1$ (supersymmetric simple pendulum) are studied. Supersymmetry can be broken due to the existence of an undetermined parameter, which is interpreted as a gauge field and appears as a firm consequence of quantization on a space with a nontrivial topology such as $S^1$. The breaking does not depend on the leading term of the superpotential, contrary to the usual case. The mechanism of supersymmetry breaking is similar to that through boundary conditions of fields in supersymmetric quantum field theory on compactified space. The supersymmetric harmonic oscillator is realized in the limit of the infinite radius of $S^1$ with the strength of the oscillator being constant.

hep-th↗

arXiv1999

A New Mechanism of Spontaneous SUSY Breaking

We propose a new mechanism of spontaneous supersymmetry breaking. The existence of extra dimensions with nontrivial topology plays an important role. We investigate new features resulted from the mechanism in two simple supersymmetric Z_2 and U(1) models. One of remarkable features is that there exists a phase in which the translational invariance for the compactified directions is broken spontaneously, accompanying the breakdown of the supersymmetry. The mass spectrum of the models appeared in reduced dimensions is a full of variety, reflecting the highly nontrivial vacuum structure of the models. The Nambu-Goldstone bosons (fermions) associated with breakdown of symmetries are found in the mass spectrum. Our mechanism also yields quite different vacuum structures if models have different global symmetries.

hep-th↗

arXiv1999

Spontaneously Broken Translational Invariance of Compactified Space

We propose a mechanism to break the translational invariance of compactified space spontaneously. As a simple model, we study a real $ϕ^4$ model compactified on $M^{D-1}\otimes S^1$ in detail, where we impose a nontrivial boundary condition on $ϕ$ for the $S^1$-direction. It is shown that the translational invariance for the $S^1$-direction is spontaneously broken when the radius $R$ of $S^1$ becomes larger than a critical radius $R^*$ and also that the model behaves like a $ϕ^4$ model on a single kink background for $R \to \infty$. It is pointed out that spontaneous breakdown of translational invariance is accompanied by that of some global symmetries, in general, in our mechanism.

hep-th↗

arXiv1999

Spontaneous Supersymmetry Breaking from Extra Dimensions

We propose a new spontaneous supersymmetry breaking mechanism, in which extra compact dimensions play an important role. To illustrate our mechanism, we study a simple model consisting of two chiral superfields, where one spatial dimension is compactified on a circle $S^1$. It is shown that supersymmetry is spontaneously broken irrespective of the radius of the circle, and also that the translational invariance for the $S^1$-direction and a global symmetry are spontaneously broken when the radius becomes larger than a critical radius. These results are expected to be general features of our mechanism. We further discuss that our mechanism may be observed as the O'Raifeartaigh type of supersymmetry breaking at low energies.

hep-th↗

arXiv1998

Softly Broken Supersymmetric Gauge Theories through Compactifications

Effects of boundary conditions of fields for compactified space directions on the supersymmetric gauge theories are discussed. For general and possible boundary conditions the supersymmetry is explicitly broken to yield universal soft supersymmetry breaking terms, and the gauge symmetry of the theory can also be broken through the dynamics of non-integrable phases, depending on number and the representation under the gauge group of matters. The 4-dimensional supersymmetric QCD is studied as a toy model when one of the space coordinates is compactified on $S^1$.

hep-th↗

arXiv1996

Profile of the Electroweak Bubble Wall

We study the CP-violating bubble wall by solving the coupled equations of motion derived from the two-Higgs-doublet model for the moduli $ρ_i$ and phases $θ_ i$ of the two scalars $(i=1,2)$ at the transition temperature. We find a solution that the CP-violating phase $θ\equivθ_1-θ_2$ connecting the CP-conserving vacua strongly violates CP in the intermediate region while the moduli largely deviate from the kink shape there. We estimate the chiral charge flux through the wall surface, which may be efficient enough to produce the baryon asymmetry by the sphaleron process.

hep-ph↗

arXiv1995

A Cutoff Constrained by the Oblique Parameters in Electroweak Theory with Two Massless Higgs Doublets

Electroweak theory with two massless Higgs doublets is studied by solving renormalization group equations for coupling constants in one-loop approximation. A cutoff~$Λ$, at which one of quartic couplings in the Higgs potential blows up, is obtained by imposing constraints from the oblique parameter $T$ on the quartic couplings at low energy. We find $Λ\simeq 0.52\sim 8.4$~TeV at the Higgs mass $M_H=100$ GeV. The cutoff $Λ$ is at most about $60$ TeV even if we take into account the LEP lower bound of $M_H\simeq 64$ GeV. It cannot reach the Planck or GUT scale due to severe experimental constraints. It is impossible in the model to realize a large gauge hierarchy as suggested many years ago by S. Weinberg.

hep-ph↗

arXiv1995

CP-Violating Profile of the Electroweak Bubble Wall

In any scenario of the electroweak baryogenesis, the profile of the CP violating bubble wall, created at the first-order phase transition, plays an essential role. We attempt to determine it by solving the equations of motion for the scalars in the two-Higgs-doublet model at the transition temperature. According to the parameters in the potential, we found three solutions. Two of them smoothly connect the CP-violating broken phase and the symmetric phase, while the other connects CP-conserving vacua but violates CP in the intermediate region. We also estimate the chiral charge flux, which will be turned into the baryon density in the symmetric phase by the sphaleron process.

hep-ph↗

arXiv1995

Chiral Charge Flux and Electroweak Baryogenesis

By treating CP-violating interaction of the electroweak bubble wall as a perturbative term, chiral charge flux through the bubble wall is estimated. It is found that the absolute value of the flux $F_Q$ has a sharp peak at $m_0 \sim a \sim T$ with $F_Q/(u T^3) \sim 10^{-3}\, (Q_L-Q_R)\,Δθ$. Here $m_0$ is the fermion mass, $1/a$ is the wall thickness, $T$ is the temperature at which the bubbles are growing, $u$ is the wall velocity, $Q_{L(R)}$ is the chiral charge of the relevant left(right)-handed fermion and $Δθ$ is the measure of CP violation.

hep-ph↗

arXiv1994

Fermion Scattering off a CP-Violating Electroweak BubbleWall II

By treating CP-violating interaction as a perturbative term, we solved in a previous paper the Dirac equation in the background of electroweak bubble wall, and obtained the transmission and reflection coefficients for a chiral fermion incident from the symmetric-phase region. We give the transmission and reflection coefficients under the other boundary condition, that is, the case of the fermion incident from the broken-phase region. There hold the respective sets of unitarity relations and also reciprocity relations among them. These relations enable us to obtain a simple form of quantum-number flux through the bubble wall, which is the first order quantity of the CP violation. A factor in the integrand of the flux, which originates from the CP violation, is very sensitive to the functional form of the CP-violating phase. The absolute value of this factor is found to decrease as $m_0/a$ increases for $m_0/a {}~\roughly{>}~1$, where $1/a$ is the wall thickness and $m_0$ the fermion mass near the critical temperature.

hep-ph↗

arXiv1994

Fermion Scattering off Electroweak Bubble Wall and Baryogenesis

By treating CP-violating interaction as a perturbative term, we solve the Dirac equation in the background of electroweak bubble wall (the distorted wave Born approximation). We obtain the transmission and reflection coefficients for a chiral fermion incident from the symmetric-phase region and for the one from the broken-phase region respectively. There hold the respective sets of unitarity relations and also reciprocity relations among them. These relations enable us to rigorously derive quantum-number flux through the bubble wall, which is the first order quantity of the CP violation. The flux is found to be negligible for a thick wall such that $m_0/a\gsim 2$, where $1/a$ is the wall thickness and $m_0$ is the fermion mass.

hep-ph↗

arXiv1994

Fermion Scattering off CP-Violating Electroweak Bubble Wall

A general prescription to solve the Dirac equation in the presence of CP-violating electroweak bubble wall is presented. The profile of the bubble wall is not specified except that the wall height is $m_0$ and zero deep in the broken- and the symmetric-phase regions, respectively, where $m_0$ is a fermion mass given by the Higgs-vacuum-expectation value and the Yukawa coupling. The CP-violating effects are evaluated by regarding CP-violating part of the bubble wall as a perturbation to CP-conserving solutions. The basic quantity, $R_{R\rightarrow L}-\bar R_{R\rightarrow L}$, which would contribute to the cosmological baryon asymmetry, is estimated for some typical profiles of the wall, where $R_{R\rightarrow L}$($\bar R_{R\rightarrow L}$) is the reflection coefficient of right-handed chiral fermion (anti-fermion).

hep-ph↗