arXiv subjects

Nobuhiro Uekusa

Publications and source records attributed to Nobuhiro Uekusa.

32 records · Page 2Linked to original sources

arXiv2008

Gauge and Yukawa couplings in 6D supersymmetric SU(6) models

We study six-dimensional (6D) SU(6) supersymmetric models where the doublet-triplet splitting, quark-lepton mass relations and gaugino-mediated supersymmetry breaking are taken into account. We find that effective 4D gauge coupling constants have highly nontrivial behavior between two compactification scales. It is shown that realistic patterns of Yukawa coupling constants are obtained for valid values of parameters and that hierarchical numbers are generated via suppression by extra-dimensional effects.

hep-ph↗

arXiv2007

Supersymmetry breaking by constant superpotentials and O'Raifeartaigh model in warped space

Supersymmetry breaking together by constant boundary superpotentials and by the O'Raifeartaigh model is studied in a warped space model. It is shown that the contribution of constant boundary superpotentials enables the moduli of chiral supermultiplets to be stabilized and that the vacuum at the stationary point has zero cosmological constant in a wide region of parameters.

hep-th↗

arXiv2007

Circumventing the No-Go Theorem in Noncommutative Gauge Field Theory

Stringent restrictions for model building are imposed by a no-go theorem in noncommutative gauge field theory. Circumventing this theorem is crucial for the construction of realistic models of particle interactions. To this end, the noncommutative construction of tensor representations of gauge groups using half-infinite Wilson lines is extended to allow for gauge groups consisting of an arbitrary number of $U_*(N)$ factors. This as well allows representations other than the ones permitted by the no-go theorem.

hep-th↗

arXiv2007

Supersymmetry Breaking and Radius Stabilization by Constant Boundary Superpotentials in Warped Space

Supersymmetry breaking and radius stabilization by constant superpotentials localized at boundaries is studied in a supersymmetric warped space model where a hypermultiplet, a compensator and a radion multiplet are taken into account. Soft mass induced by the anomaly mediation can be of the order of 100GeV and can be dominant compared to that mediated by bulk fields. A lighter physical mode composed of the radion and the moduli can have mass of the order of a TeV and the gravitino mass can be of the order of 10^7 GeV. The radius is stabilized by the presence of the constant boundary superpotentials. We also find that the mass splitting has an interesting dependence on the bulk mass parameter c.

hep-th↗

arXiv2007

Selecting Gauge Theories on an Interval by 5D Gauge Transformations

Gauge symmetry breaking by boundary conditions is studied in a general warped geometry in five dimensions. It has been suggested that a wider class of boundary conditions is allowed by requiring only vanishing surface terms when deriving the field equations for gauge theories on an interval (i.e., employing a variational principle), in comparison to the twist in orbifolding with automorphisms of the Lie algebra. We find that there are classes of boundary conditions allowed by the variational principle which violate the Ward-Takahashi identity and give four-point tree amplitudes that increase with energy in channels that have not yet been explored, leading to cross sections that increase as powers of the energy (which violates the tree level unitarity). We also find that such boundary conditions are forbidden by the requirement that the definitions of the restricted class of five-dimensional (5D) gauge transformations be consistent.

hep-th↗

arXiv2007

Radius stabilization by constant boundary superpotentials in warped space

A warped space model with a constant boundary superpotential has been an efficient model both to break supersymmetry and to stabilize the radius, when hypermultiplet, compensator and radion multiplet are taken into account. In such a model of the radius stabilization, the radion and moduli masses, the gravitino mass and the induced soft masses are studied. We find that a lighter physical mode composed of the radion and the moduli can have mass of the order of a TeV and that the gravitino mass can be of the order of 10$^7$ GeV. It is also shown that soft mass induced by the anomaly mediation can be of the order of 100GeV and can be dominant compared to that mediated by bulk fields. Localized F terms and D terms are discussed as candidates of cancelling the cosmological constant. We find that there is no flavor changing neutral current problem in a wide range of parameters.

hep-th↗

arXiv2007

Dependence of SU(N) coupling behavior on the size of extra dimensions

Coupling constants at high energy scales are studied in SU(N) gauge theory with distinct sizes of extra dimensions. We present the solution of gauge couplings as functions of the energy in such a way as to track the number of Kaluza-Klein modes. In a flat extra dimension, it is shown that the gauge couplings have logarithmic dependence on the size of the extra dimension and linear dependence on the number of Kaluza-Klein modes. We find some patterns of the dependence on flavor of bulk and brane fermions. Dependence of gauge couplings on the size of an extra dimension is discussed also in a warped extra dimension.

hep-th↗

arXiv2006

Supersymmetry Breaking by Constant Boundary Superpotentials in Warped Space

Supersymmetry breaking by constant (field independent) superpotentials localized at boundaries is studied in a supersymmetric warped space model. We calculate the Kaluza-Klein mass spectrum of the hypermultiplet. We take into account of the radion and the compensator supermultiplets, as well as the bulk mass $c$ for the hypermultiplet. The mass splitting is similar to that of the Scherk-Schwarz supersymmetry breaking (in flat space) for large $|c|$, and has an interesting dependence on the bulk mass parameter $c$. We show that the radius is stabilized by the presence of the constant boundary superpotentials.

hep-th↗

arXiv2006

Localized Kaluza-Klein Graviton and Cosmological Constant

We study linearized graviton in the presence of a four-dimensional cosmological constant in two brane models with a warped extra dimension. In explicit models including bulk scalar fields, we calculate the masses of Kaluza-Klein modes of graviton and their interactions with matter on the visible brane. It is shown that the effects of the cosmological constant contribute by the equivalent size to the warp factor, masses and couplings and that bulk scalar fields can increase the effects. This is examined further independently of the forms of scalar potentials. Then it is found how the masses and couplings are described in terms of the warp factors and generic scalar potentials. A possibility that the masses and couplings are significantly changed by cosmological constant effects is discussed.

hep-ph↗

arXiv2005

Asymmetry and Minimality of Quark Mass Matrices

We systematically investigate general forms of mass matrices for three-generation up and down quarks, including asymmetrical ones in generation space. Viable zero matrix elements are explored which are compatible with the current observation of masses and mixing angles, and also with the recent measurement of CP violation in the B-meson system. The simplest form with the maximal number of vanishing matrix elements is found to be almost consistent with the experimental data, but has a scratch that one of the mixing angle is slightly large. At the next-to-minimal level, it is found with a help of leptonic generation mixing that only six patterns of mass matrices well describe the experimental data. These sets of mass textures predict all the properties of quarks, including the CP violation, as well as the large (charged) lepton mixing, which may be appropriate for the atmospheric neutrino in grand unification scheme.

hep-ph↗

arXiv2005

Flavor quark at high temperature from a holographic model

Gauge theory with light flavor quark is studied by embedding a D7 brane in a deconfinement phase background newly constructed. We find a phase transition by observing a jump of the vacuum expectation value of quark bilinear and also of the derivative of D7 energy at a critical temperature. For the model considered here, we also study quark-antiquark potential to see some possible quark-bound states and other physical quantities in the deconfinement phase.

hep-th↗

arXiv2003

Effective de Sitter brane via running radius

We present the solution for effective couplings on a running de Sitter brane. A renormalization group formalism is developed for linearized gravity in a two de Sitter brane model. It is shown that the effective tension remains a constant similarly to the zero cosmological constant case. We also discuss the suppression of higher derivative terms.

hep-th↗

arXiv2003

Dilaton coupled brane-world and field trapping

We address solutions of brane-world with cosmological constant $λ$ by introducing the dilaton in 5d bulk, and we examine the localization of graviton, gauge bosons and dilaton. For those solutions, we find that both graviton and gauge bosons can be trapped for either sign, positive or negative, and wide range of $λ$ due to the non-trivial dilaton. While the dilaton can not be trapped on the brane.

hep-th↗

arXiv2003

Gauge symmetry and cosmological constant on a brane

We have examined the localization of gauge bosons on the three-brane embedded in 5D bulk space-time, and we find two kinds of branes on which both graviton and gauge bosons can be trapped. One is the dS brane with a positive cosmological constant, and the other is the one with zero cosmological constant or 4D Minkowski brane. Then, which brane is realized would depend on the observation of the cosmological constant of our world.

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