arXiv subjects

Naoyuki Haba

Publications and source records attributed to Naoyuki Haba.

At least 109 records · Page 6Linked to original sources

arXiv2008

Tri-bimaximal Mixing from Cascades

We study fermion mass matrices of the cascade form which are compatible with the tri-bimaximal lepton mixing and generation mass hierarchy. The flat-cascade lepton matrices imply a parameter-independent relation among the mixing angles and mass eigenvalues. The relation has several indications that the atmospheric neutrino mixing angle is close to maximal and the other two angles have a correlation independently of neutrino mass eigenvalues. We also discuss phenomenological aspects of the cascade matrices; flavor-violating rare decays of charged leptons, thermal leptogenesis, and leptonic CP violation. Possible dynamical origins of the cascades are illustrated based on flavor symmetry and in higher-dimensional theory.

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arXiv2008

Dynamical Rearrangement of Theta Parameter in Presence of Mixed Chern-Simons Term

We study the five-dimensional SU(3)_c x U(1)_C gauge theory on the orbifold S^1/Z_2 with a mixed Chern-Simons term. We particularly pay attention to the realization of the dynamical rearrangement of the theta parameter for SU(3)_c. It is shown that the physics remains invariant under a large gauge transformation which even changes the action, completely removing the theta parameter, because of the Hosotani mechanism for the U(1)_C gauge interactions. In other words, we show that the theta parameter can be regarded as a boundary condition for the orbifolding in light of the dynamical rearrangement.

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arXiv2008

iGUT: Grand Unified Theory on Interval

We investigate a construction of five-dimensional (5D) grand unified theories (GUTs) on an interval, which we call iGUTs. We analyze supersymmetric SO(10) iGUT as an example, where the gauge multiplet is spread over the 5D bulk. The SO(10) is directly reduced to the standard model gauge symmetry through the interval boundary conditions. Notice that this rank reduction is impossible in case of GUTs on orbifolds. Four scenarios are possible according to locations (bulk or brane) of Higgs and matter fields. We investigate the gauge-coupling unification, the proton decay, the SO(10) GUT features such as t-b-tau unification and so on in each scenario. We also comment on the flavor phenomenology.

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arXiv2008

Meta-stable SUSY Breaking Model in Supergravity

We analyze a supersymmetry (SUSY) breaking model proposed by Intriligator, Seiberg and Shih in a supergravity (SUGRA) framework. This is a simple and natural setup which demands neither extra superpotential interactions nor an additional gauge symmetry. In the SUGRA setup, the U(1)R symmetry is explicitly broken by the constant term in the superpotential, and pseudo-moduli field naturally takes non-zero vacuum expectation value through a vanishing cosmological constant condition. Sfermions tend to be heavier than gauginos, and the strong-coupling scale is determined once a ratio of sfermion to gaugino masses is fixed.

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arXiv2008

Effective Potential of Higgs Field in Warped Gauge-Higgs Unification

The gauge-Higgs unification is one of influential scenarios to solve the hierarchy problem in the Standard Model. Recently, the scenario on the warped background attracts many attentions due to a large possibility to construct a realistic model naturally in this framework. It is, however, well known that the effective potential for the Higgs field, which is the most important prediction of the scenario, is not easy to calculate on the warped background, because masses of Kaluza-Klein particles are not obtained analytically. In this article, we derive useful formulae for the effective potential. The formulae allow us to calculate the Higgs mass easily, thus to construct a realistic model in the gauge-Higgs unification scenario on the warped background. Using obtained formulae, we calculate contributions from bulk fermions with several boundary conditions. We also show bulk fermions, which have boundary conditions not allowed in the orbifold picture, do not contribute to the effective potential.

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arXiv2008

New contribution to dimension five operators on proton decay in anomaly mediation scenario

In supergravity, effective superpotential relevant to dimension five operators on proton decay processes also leads to supersymmetry breaking terms among sfermions, dimension four operators. These dimension four operators induce the dimension five operators through 1-loop diagrams dressed by gauginos. We find that, in a class of models with the anomaly mediation, the 1-loop contributions can be comparable to those at the tree level. Therefore, such operators have a great impact on proton decay rate. Depending on a universal phase of gaugino masses and soft mass spectrum, the proton decay rate can be enhanced or suppressed.

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arXiv2008

F-term Induced Flavor Mass Spectrum

New mechanism of generating flavor mass spectrum is proposed by using an O'Raifeartaigh-type supersymmetry breaking model. A desired bilinear form of fermion mass spectrum is naturally realized through F-components of gauge-singlet (nonet of SU(3) flavor symmetry) superfields, and the suitable charged-lepton mass relation is reproduced. The charged-slepton mass spectrum is non-degenerate in general, and can be even hierarchical (proportional to the charged-lepton masses in the specific case). Flavor changing neutral processes are suppressed since the charged-lepton and slepton (except for right-handed sneutrino) mass matrices are diagonalized simultaneously in the flavor space. The right-handed sneutrinos are light with the similar ratio to the lepton sector ($\tilde{m}_{ν_R}$/$\tilde{m}_e \sim m_ν$/$m_e$).

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arXiv2007

A Simple Model of Direct Gauge Mediation of Metastable Supersymmetry Breaking

We construct a model of direct gauge mediation of metastable SUSY breaking by simply deforming the Intriligator, Seiberg and Shih model in terms of a dual meson superpotential mass term. No extra matter field is introduced. The deformation explicitly breaks a U(1)_R symmetry and a pseudo moduli have a nonzero VEV at one-loop. Our metastable SUSY breaking vacuum turns out to be sufficiently long-lived. By gauging a subgroup of flavor symmetry, our model can directly couple to the standard model, which leads to nonvanishing gaugino mass generation. It is also shown that our model can evade the Landau pole problem. We show the parameters in the SUSY breaking sector are phenomenologically constrained.

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arXiv2007

New Origin of a Bilinear Mass Matrix Form

The charged lepton mass formula can be explained when the masses are propotinal to the squared vacuum expectation values (VEVs) of scalar fields. We introduce U(3) flavor symmetry and its nonet scalar field $Φ$, whose VEV structure plays an essential role for generating the fermion mass spectrum. We can naturally obtain bilinear form of the Yukawa coupling $Y_{ij} \propto \sum_k <Φ_{ik}> <Φ_{kj}>$ without the non-renormalizable interactions, when the flavor symmetry is broken only through the Yukawa coupling and tadpole terms. We also speculate the possible VEV structure of $<Φ>$.

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arXiv2006

Family Symmetry and Single Right-Handed Neutrino Dominance in Five Dimensions

We consider several neutrino mass models in an extra-dimensional setting on a quantitative level. All the models are set in a five-dimensional scenario, with the standard model (SM) particles living on a brane, while three additional SM gauge singlets live in the bulk of an extra dimension, which is compactified on a S^1/Z_2 orbifold. The spontaneous breaking of an additional, continuous U(1) family symmetry is used to generate suitable neutrino mass matrices via single right-handed neutrino dominance through the corresponding five-dimensional extension of the see-saw mechanism. In this manner possible problems of this combination for some models in four dimensions could be overcome. The considered models differ with respect to the charges under the family symmetry and the nature of the five-dimensional Majorana mass term.

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arXiv2006

Vanishing dimension five proton decay operators in the SU(5) SUSY GUT

We propose a natural framework of SU(5) supersymmetric grand unified theory with the minimal particle contents, which does not contain dimension five proton decay operators. The suitable fermion mass hierarchy can be reproduced by higher dimensional operators of an adjoint Higgs field which breaks SU(5) gauge symmetry.

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arXiv2006

A universal seesaw mechanism in five dimensions

We show the universal seesaw in the extra dimension setup, where three extra vector-like fields exist in the 5D bulk with heavy masses. We take the framework of the left-right symmetric model. The universal seesaw formula is easily obtained as a replacement of the vector-like mass in 4D case M_i to 2 M_* tan[pi RM_i] (M_*: 5D Planck scale, M_i: vector-like bulk mass, and R: compactification radius). The smallness of Dirac neutrino mass can be naturally explained in the 5D setup. We also show the Majorana neutrino case.

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arXiv2006

Invisible Technicolor

We propose a scenario of dynamical electroweak symmetry breaking which is applicable to the model with no tree-level potential for the elementary Higgs doublet field. An example of such a model is the gauge-Higgs unification model. The strong coupling "technicolor" dynamics can provide the scale of the electroweak symmetry breaking in the potential of the Higgs doublet field. The negative mass squared and quartic coupling can be generated through the Yukawa couplings among heavy and light "technifermions" and the Higgs doublet field. Since the massless "technifermion" is singlet under the electroweak gauge symmetry, no large corrections to the electroweak observables arise. As a prediction of this scenario, there must be a pseudo-Nambu-Goldstone boson which couple with the Higgs field in a specific way, though it is singlet under the standard model gauge symmetry.

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arXiv2006

A Supersymmetric Contribution to the Neutrino Mass Matrix and Breaking of mu-tau Symmetry

Supersymmetry broken by anomaly mediation suffers from tachyonic slepton masses. A possible solution to this problem results in "decoupling", i.e., the first two generations of sfermions are much heavier than the third one. We note that in this scenario a sizable loop-induced contribution to the neutrino mass matrix results. As an application of this scenario we take advantage of the fact that the decoupling evidently not obeys 2-3 generation exchange symmetry. In the neutrino sector, this 2-3 symmetry (or mu-tau symmetry) is a useful Ansatz to generate zero theta_{13} and maximal theta_{23}. The induced deviations from these values are given for some examples, thereby linking SUSY breaking to the small parameters (including possibly the solar mass splitting) of the neutrino sector.

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arXiv2006

5D seesaw, flavor structure, and mass textures

In the 5D theory in which only 3 generation right-handed neutrinos are in the bulk, the neutrino flavor mixings and the mass spectrum can be constructed through the seesaw mechanism. The 5D seesaw is easily calculated just by a replacement of the Majorana mass eigenvalues, M_i, by 2 M_*tan(h)[πRM_i] (M_*: 5D Planck scale, R: compactification radius). The 5D features appear when the bulk mass, which induces the 4D Majorana mass, is the same as the compactification scale or larger than it. Depending on the type of bulk mass, the seesaw scales of the 3 generations are strongly split (the tan-function case) or degenerate (the tanh-function case). In the split case, the seesaw enhancement is naturally realized. The single right-handed neutrino dominance works in a simple setup, and some specific mass textures, which are just assumptions in the 4D setup, can be naturally obtained in 5 dimensions. The degenerate case is also useful for a suitable neutrino flavor structure.

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arXiv2006

Twisted Flavors and Tri/bi-Maximal Neutrino Mixing

A new framework for handling flavor symmetry breaking in the neutrino sector is discussed where the source of symmetry breaking is traced to the global property of right-handed neutrinos in extra-dimensional space. Light neutrino phenomenology has rich and robust predictions such as the tri/bi-maximal form of generation mixing, controlled mass spectrum, and no need of flavor mixing couplings in the theory.

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arXiv2006

Discrete Flavor Symmetry, Dynamical Mass Textures, and Grand Unification

Discrete flavor symmetry is explored for an intrinsic property of mass matrix forms of quarks and leptons. In this paper we investigate the S3 permutation symmetry and derive the general forms of mass matrices in various types of S3 theories. We also exhibit particular realizations of previous ansatze of mass matrices, which have often been applied in the literature to the standard model Yukawa sector. Discrete flavor symmetry is also advantageous for vanishing matrix elements being dynamically generated in the vacuum of scalar potential. This is due to the fact that group operations are discrete. While zero elements themselves do not explain mass hierarchies, we introduce an abelian flavor symmetry. A non-trivial issue is whether successful quantum numbers can be assigned so that they are compatible with other (non-abelian) flavor symmetries. We show typical examples of charge assignments which not only produce hierarchical orders of mass eigenvalues but also prohibit non-renormalizable operators which disturb the hierarchies in first-order estimation. As an explicit application, a flavor model is constructed in grand unification scheme with S3 and U(1) (or Z_N) flavor symmetries.

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arXiv2006

Split-SUSY versus SUSY GUTS

The gauge coupling unification is one of main motivations in the split-SUSY scenario, and the existence of the grand unified theories (GUTs) is assumed. We examine how to realize split-SUSY mass spectrum in the context of GUTs and find that the construction of split-SUSY GUTs is by no means straightforward. With R-symmetry breaking sources in the GUT sector, GUT particles play a role of the messengers in the gauge mediation scenario and their contributions to gaugino masses can be sizable. We find the upper bound on soft scalar masses of O(10^{10}) GeV from consistency for constructing the split-SUSY GUT. Also, we discuss the attempt to construct R-symmetric GUT models.

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