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Toshifumi Yamashita

Publications and source records attributed to Toshifumi Yamashita.

46 records · Page 3Linked to original sources
arXiv2004

Dynamical symmetry breaking in Gauge-Higgs unification of 5D ${\mathcal N}=1$ SUSY theory

We study the dynamical symmetry breaking in the gauge-Higgs unification of the 5D ${\mathcal N}=1$ SUSY theory, compactified on an orbifold, $S^1/Z_2$. This theory identifies Wilson line degrees of freedoms as ``Higgs doublets''. We consider $SU(3)_c \times SU(3)_W$ and SU(6) models, in which the gauge symmetries are reduced to $SU(3)_c \times SU(2)_L \times U(1)_Y$ and $SU(3)_c \times SU(2)_L \times U(1)_Y \times U(1)$, respectively, through the orbifolding boundary conditions. Quarks and leptons are bulk fields, so that Yukawa interactions can be derived from the 5D gauge interactions. We estimate the one loop effective potential of ``Higgs doublets'', and analyze the vacuum structures in these two models. We find that the effects of bulk quarks and leptons destabilize the suitable electro-weak vacuum. We show that the introduction of suitable numbers of extra bulk fields possessing the suitable representations can realize the appropriate electro-weak symmetry breaking.

hep-ph↗
arXiv2004

A general formula of the effective potential in 5D SU(N) gauge theory on orbifold

We show a general formula of the one loop effective potential of the 5D SU(N) gauge theory compactified on an orbifold, $S^1/Z_2$. The formula shows the case when there are fundamental, (anti-)symmetric tensor and adjoint representational bulk fields. Our calculation method is also applicable when there are bulk fields belonging to higher dimensional representations. The supersymmetric version of the effective potential with Scherk-Schwarz breaking can be obtained straightforwardly. We also show some examples of effective potentials in SU(3), SU(5) and SU(6) models with various boundary conditions, which are reproduced by our general formula.

hep-ph↗
arXiv2004

Dynamical symmetry breaking in Gauge-Higgs unification on orbifold

We study the dynamical symmetry breaking in the gauge-Higgs unification of the 5D theory compactified on an orbifold, $S^1/Z_2$. This theory identifies Wilson line degrees of freedoms as ``Higgs doublets''. We consider $SU(3)_c \times SU(3)_W$ and SU(6) models with the compactification scale of order a few TeV. The gauge symmetries are reduced to $SU(3)_c \times SU(2)_L \times U(1)_Y$ and $SU(3)_c \times SU(2)_L \times U(1)_Y \times U(1)$, respectively, through the orbifolding boundary conditions. We estimate the one loop effective potential of ``Higgs doublets'', and find that the electro-weak breaking is realized through the radiative corrections when there are suitable numbers of bulk fields possessing the suitable representations. The masses of ``Higgs doublets'' are ${\mathcal O}(100)$ GeV in this scenario.

hep-ph↗
arXiv2003

Sliding Singlet Mechanism Revisited

We show that the unification of the doublet Higgs in the standard model (SM) and the Higgs to break the grand unified theory (GUT) group stabilizes the sliding singlet mechanism which can solve the doublet-triplet (DT) splitting problem. And we generalize this attractive mechanism to apply it to many unified scenarios. In this paper, we try to build various concrete E_6 unified models by using the generalized sliding singlet mechanism.

hep-ph↗
arXiv2003

E_6 Unification, Doublet-Triplet Splitting and Anomalous U(1)_A Symmetry

We propose a natural Higgs sector in E_6 grand unified theory (GUT) with anomalous U(1)_A gauge symmetry. In the scenario, the doublet-triplet splitting can be realized while the proton decay via dimension 5 operator is suppressed. The gauge coupling unification is also realized without finetuning. The GUT scale is generally lower than the usual GUT scale 2\times 10^{16} GeV, the proton decay via dimension 6 operator can be seen in near future experiment. The lifetime of nucleon in the model is roughly estimated as τ_p(p\to e^+π^0)\sim 3\times 10^{33} years. It is shown that the Higgs sector is compatible with the matter sector proposed by one of the authors, which reproduces the realistic quark and lepton mass matrices including bi-large neutrino mixing angle. Combining the Higgs sector and the matter sector, we can obtain the totally consistent E_6 GUT. The input parameters are only 8 integer anomalous U(1)_A charges (+3 for singlet Higgs) for the Higgs sector and 3 (half) integer charges for the matter sector.

hep-ph↗
arXiv2003

Flipped SO(10) model

We show that as in the flipped SU(5) models, doublet-triplet splitting is realized by the missing partner mechanism in the flipped SO(10) models. The gauge group $SO(10)_F\times U(1)_{V'_F}$ includes $SU(2)_E$ gauge symmetry, that plays an important role in solving supersymmetric flavor problem by introducing non-abelian horizontal gauge symmetry and anomalous $U(1)_A$ gauge symmetry. The gauge group can be broken into the standard model gauge group by VEVs of only spinor fields, such models may be easier than $E_6$ models to be derived from the superstring theory.

hep-ph↗
arXiv2003

Simple $E_6$ Unification with Anomalous $U(1)_A$ Symmetry

We propose simpler Higgs sectors in $E_6$ grand unified theory with anomalous $U(1)_A$ gauge symmetry than the previous model in Ref.1). As in the previous model, the doublet-triplet splitting can be realized in a natural way, while proton decay via dimension 5 operators is suppressed and gauge coupling unification is also realized without fine-tuning. Combining the matter sector, simple complete GUTs can be obtained. Since the Higgs sector is simpler, the gauge coupling constant at the cutoff scale can be in perturbative region, and therefore, the estimated value of the lifetime of a nucleon in this model, $τ_p(p\to e^+π^0)\sim 5\times 10^{33}$ years, becomes more reliable.

hep-ph↗
arXiv2003

Gauge Coupling Unification in GUT with Anomalous U(1) Symmetry

We show that in the framework of grand unified theory (GUT) with anomalous $U(1)_A$ gauge symmetry, the success of the gauge coupling unification in the minimal SU(5) GUT is naturally explained, even if the mass spectrum of superheavy fields does not respect SU(5) symmetry. Because the unification scale for most realizations of the theory becomes smaller than the usual GUT scale, it suggests that the present level of experiments is close to that sufficient to observe proton decay via dimension 6 operators, $p\to e+π$.

hep-ph↗
arXiv2002

Two-Loop Analysis of Gauge Coupling Unification with Anomalous U(1) Symmetry and Proton Decay

Recently, a new mechanism, which explains why the three gauge coupling constants meet at a certain scale in the minimal supersymmetric standard model, has been proposed in a scenario of grand unified theories with anomalous $U(1)_A$ gauge symmetry. It is a non-trivial result that although there are many superheavy fields whose mass scales are below the unification scale, this mechanism explains this fact by means of one-loop renormalization group equations. Since the unification scale generically becomes below the usual GUT scale, $2\times 10^{16}$ GeV, and proton decay via dimension 5 operators is suppressed, the scenario predicts that proton decay via dimension 6 operators, $p\to e π^0$, will be observed in the near future. In this paper, we attempt to estimate a reasonable range of values of the lifetime of the proton predicted within this scenario by using a two-loop renormalization group calculation and the ambiguities of \order1 coefficients.

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