Fermion Mass Hierarchy Research Articles

Signals from extra dimensions decoupled from the compactification scale

Multilocalization provides a simple way of decoupling the mass scale of new physics from the compactification scale of extra dimensions. It naturally appears, for example, when localization of fermion zero modes is used to explain the observed fermion spectrum, leaving low energy remnants of the geometrical origin of the fermion mass hierarchy. We study the phenomenology of the simplest five dimensional model with order one Yukawa couplings reproducing the standard fermion masses and mixing angles and with a light Kaluza-Klein quark Q_{2/3} saturating experimental limits on V_{tb} and m_Q, and then with observable new effects at Tevatron.

New origin for approximate symmetries from distant breaking in extra dimensions

The recently proposed theories with TeV-scale quantum gravity remove the usual ultraviolet desert between $\sim 10^{3} - 10^{19}$ GeV where effective field theory ideas apply. Consequently, the success of the desert in explaining approximate symmetries is lost, and theories of flavor, neutrino masses, proton longevity or supersymmetry breaking, lose their usual habitat. In this paper we show that these ideas can find a new home in an infrared desert: the large space in the extra dimensions. The main idea is that symmetries are primordially exact on our brane, but are broken at O(1) on distant branes. This breaking is communicated to us in a distance-suppressed way by bulk messengers. We illustrate these ideas in a number of settings: 1) We construct theories for the fermion mass hierarchy which avoid large FCNC's. 2) We re-iterate that proton stability can arise if baryon number is gauged in the bulk. 3) We study experimental constraints on light gauge fields and scalars in the bulk. 4) We remark that the same ideas can be used to explain small neutrino masses, and hierarchical supersymmetry breaking. 5) We construct a theory with bulk technicolor, avoiding the difficulties with extended technicolor. There are also interesting experimental signals of these ideas: 1) Attractive or repulsive, isotope dependent sub-millimeter forces $\sim 10^6$ times gravitational strength, from the exchange of light bulk particles. 2) Novel Higgs decays to light generation fermions plus bulk scalars. 3) Collider production of bulk vector and scalar fields, leading to large $\gamma$ or jet+ missing energy signals.

Fermion Mass Hierarchy in the Grand Unified Theory on an S1/(Z2 xZ2') Orbifold

We suggest a simple grand unified theory where the fifth dimensional coordinate is compactified on an $S_1/(Z_2 \times Z_2')$ orbifold. This model is based on the supersymmetric flipped $SU(5) \times U(1)$ grand unified theory, which can realize not only the triplet-doublet splitting but also the natural fermion mass hierarchies. The triplet-doublet splitting is realized by $S_1/(Z_2 \times Z_2')$ orbifolding, which also reduces the gauge group as $SU(5) \times U(1) \to SU(3)_c \times SU(2)_L \times U(1)_Z \times U(1)_X$. The suitable fermion mass hierarchies are generated by integrating out extra three sets of vector-like heavy fields which can propagate in five dimensions. The radiative corrections to the large Yukawa coupling of right-handed neutrinos can reduce the gauge group to $SU(3)_c \times SU(2)_L \times U(1)_Y$.

U(2)-like flavor symmetries and approximate bimaximal neutrino mixing

Models involving a U(2) flavor symmetry, or any of a number of its non-Abelian discrete subgroups, can explain the observed hierarchy of charged fermion masses and CKM angles. It is known that a large neutrino mixing angle connecting second and third generation fields may arise via the seesaw mechanism in these models, without a fine tuning of parameters. Here we show that it is possible to obtain approximate bimaximal mixing in a class of models with U(2)-like Yukawa textures. We find a minimal form for Dirac and Majorana neutrino mass matrices that leads to two large mixing angles, and show that our result can quantitatively explain atmospheric neutrino oscillations while accommodating the favored, large angle MSW solution to the solar neutrino problem. We demonstrate that these textures can arise in models by presenting a number of explicit examples.

Flavor Symmetry on Non-Commutative Compact Space and SU(6) x SU(2)R Model

In the four-dimensional effective theory from string compactification discrete flavor symmetries arise from symmetric structure of the compactified space and generally contain both the $R$ symmetry and non-$R$ symmetry. We point out that a new type of non-Abelian flavor symmetry can also appear if the compact space is non- commutative. Introducing the dihedral group $D_4$ as such a new type of flavor symmetry together with the $R$ symmetry and non-$R$ symmetry in $SU(6) \times SU(2)_R$ model, we explain not only fermion mass hierarchies but also hierarchical energy scales including the breaking scale of the GUT-type gauge symmetry, intermediate Majorana masses of R-handed neutrinos and the scale of $\mu$-term.

Possible flavor mixing structures of lepton mass matrices

To search for possible textures of lepton mass matrices, we systematically examine flavor mixing structures which can lead to large lepton mixing angles. We find out 37 mixing patterns are consistent with experimental data, taking into account phase factors in the mixing matrices. Only six of the patterns can explain the observed data without any tuning of parameters, while the others need particular choices for the phase values. It is found that these six mixing patterns are those predicted by the models which have been proposed to account for fermion mass hierarchies. On the other hand, the others may give new flavor mixing structures of lepton mass matrices and therefore new possibilities of model construction.

Dynamical symmetry breaking in warped compactifications

We study dynamical electroweak symmetry breaking in the Randall-Sundrum scenario. We show that one extra dimension is enough to give the correct pattern of electroweak symmetry breaking in a simple model with gauge bosons and the right-handed top quark in the bulk. The top quark mass is also in agreement with experiment. Furthermore, we propose an extended scenario with all Standard Model gauge bosons and fermions propagating in the bulk, which naturally accommodates the fermion mass hierarchies. No new fields or interactions beyond the observed in the Standard Model are required.

Neutrino Masses, Anomalous U(1) Gauge Symmetry and Doublet-Triplet Splitting

We propose an attractive scenario of grand unified theories in which doublet-triplet splitting is naturally realized in SO(10) unification using the Dimopoulos-Wilczek mechanism. The anomalous U(1)A gauge symmetry plays an essential role in the doublet-triplet splitting mechanism. It is interesting that the anomalous U(1)A charges determine the unification scale and mass spectrum of additional particles, as well as the order of the Yukawa couplings of quarks and leptons. For the neutrino sector, bi-maximal mixing angles are naturally obtained, and proton decay via dimension 5 operators is suppressed. It is suggestive that the anomalous U(1)A gauge symmetry motivated by superstring theory effectively solves the two biggest problems in grand unified theories, the fermion mass hierarchy problem and doublet-triplet splitting problem.

Cartography with accelerators: Locating fermions in extra dimensions at future lepton colliders

In the model of Arkani-Hamed and Schmaltz the various chiral fermions of the Standard Model(SM) are localized at different points on a thick wall which forms an extra dimension. Such a scenario provides a way of understanding the absence of proton decay and the fermion mass hierarchy in models with extra dimensions. In this paper we explore the capability of future lepton colliders to determine the location of these fermions in the extra dimension through precision measurements of conventional scattering processes both below and on top of the lowest lying Kaluza-Klein gauge boson resonance. We show that for some classes of models the locations of these fermions can be very precisely determined while in others only their relative positions can be well measured.

Fermion mass hierarchies and small mixing angles from extra dimensions

In this paper we study renormalization-group evolutions of Yukawa matrices enhanced by Kaluza-Klein excited modes and analyze their infrared fixed-point structure. We derive the necessary conditions to obtain hierarchies between generations on the fixed point. These conditions restrict how the fields in the models can extend to higher dimensions. Several specific mechanisms to realize the conditions are presented. We also take into account the generation mixing effects and find a scenario where the mixing angles become small at low energy even with large initial values at a high-energy scale. A toy model is shown to lead to realistic quark mass matrices.

MASS GENERATION AND THE DYNAMICAL ROLE OF THE KATOPTRON GROUP

Heavy mirror fermions along with a new strong gauge interaction capable of breaking the electroweak gauge symmetry dynamically were recently introduced under the name of katoptrons. Their main function is to provide a viable alternative to the Standard-Model Higgs sector. In such a framework, ordinary fermions acquire masses after the breaking of the strong katoptron group which allows mixing with their katoptron partners. The purpose of this letter is to study the elementary-scalars-free mechanism responsible for this breaking and its implications for the fermion mass hierarchies.

Fermion Mass Hierarchy and Small Mixing Angles from Extra Dimensions

Fermion Mass Hierarchy and Small Mixing Angles from Extra Dimensions

Large angle MSW solution in grand unified theories withSU(3)×U(1)horizontal symmetry

We construct a model with a SU(3) X U(1) horizontal symmetry in the context of Grand Unified Theories. In our models, the bi-maximal lepton mixing and suitable neutrino masses for the large angle MSW solution are obtained without any fine-tuning due to the spontaneously broken SU(3)_H symmetry. The three generations of quarks and leptons are unified as members of the SU(3)_H fundamental representation, and the U(1)_H charge gives the origin of the fermion mass hierarchy and mixing angles. We present two explicit examples of SU(5)_GUT and SO(10)_GUT models, in which the Yukawa structures are given successfully.

R-symmetry, Yukawa textures and anomaly mediated supersymmetry breaking

We explore, in the MSSM context, an extension of the Anomaly Mediated Supersymmetry Breaking solution for the soft scalar masses that is possible if the underlying theory has a gauged R-symmetry. The slepton mass problem characteristic of the scenario is resolved, and a context for the explanation of the fermion mass hierarchy provided.

Bulk fields and supersymmetry in a slice of AdS

Five-dimensional models where the bulk is a slice of AdS have the virtue of solving the hierarchy problem. The electroweak scale is generated by a ``warp'' factor of the induced metric on the brane where the standard model fields live. However, it is not necessary to confine the standard model fields on the brane and we analyze the possibility of having the fields actually living in the slice of AdS. Specifically, we study the behaviour of fermions, gauge bosons and scalars in this geometry and their implications on electroweak physics. These scenarios can provide an explanation of the fermion mass hierarchy by warp factors. We also consider the case of supersymmetry in the bulk, and analyze the conditions on the mass spectrum. Finally, a model is proposed where the warp factor generates a small (TeV) supersymmetry-breaking scale, with the gauge interactions mediating the breaking to the scalar sector.

Bi-maximal neutrino mixings and proton decay in SO(10) with anomalous flavor [formula omitted

By supplementing supersymmetric SO(10) with an anomalous U(1) flavor symmetry and additional `matter' superfields carrying suitable U(1) charges, we explain the charged fermion mass hierarchies, the magnitudes of the CKM matrix elements, as well as the solar and atmospheric neutrino data. We stress bi-maximal vacuum neutrino mixings, and indicate how the small or large mixing angle MSW solution can be incorporated. The U(1) symmetry also implies that τ p→ Kν [ SO(10)]∼(10– 100)·τ p→Kν[ minimal SU(5)] .

Natural fermion mass hierarchy and new signals for the Higgs boson

We suggest a novel approach towards resolving the fermion mass hierarchy problem within the framework of the standard model. It is shown that the observed masses and mixings can be explained with order one couplings using successive higher dimensional operators involving the SM Higgs doublet field. This scenario predicts a flavor-dependent enhancement in the Higgs boson coupling to the fermions. It also predicts a flavor changing $\overline{t}{\mathrm{ch}}^{0}$ interaction with a strength comparable to that of $\overline{b}{\mathrm{bh}}^{0},$ opening up new discovery channels for the Higgs boson at the upgraded Fermilab Tevatron and the CERN LHC. Additional tests of the framework include observable ${D}^{0}\ensuremath{-}{D}^{0}$ mixing and a host of new phenomena associated with flavor physics at the TeV scale.

R-parity violation: origin of μ-term and other consequences

We propose a new mechanism in which the generation of the supersymmetric μ -term as well charged lepton masses is closely tied to R -parity violation involving heavy vector-like families. A realistic example based on SU (3) c × SU (2) L × U (1) Y , supplemented by the symmetry R × U (1) , is presented, where R ( U (1) ) denotes a continuous R (flavor) symmetry. In addition to the μ -term, the charged fermion mass hierarchies and mixings, as well as baryon number conservation are also nicely explained. Bilinear R -parity violating coupling involving the first generation gives rise to neutrino mass relevant for the small angle ν e − ν s MSW oscillations, where ν s denotes a sterile state. The atmospheric neutrino puzzle is resolved via maximal mixing angle ν μ − ν τ oscillations. The decay of the lightest neutralino (LSP) and leptogenesis are briefly discussed.

Nonanomalous horizontalU(1)Hgauge model of flavor

A nonanomalous horizontal $\mathrm{U}{(1)}_{H}$ gauge symmetry can be responsible for the fermion mass hierarchies of the minimal supersymmetric standard model. Imposing the consistency conditions for the absence of gauge anomalies yields the following results: (i) unification of leptons and down-type quark Yukawa couplings is allowed at most for two generations; (ii) the $\ensuremath{\mu}$ term is necessarily somewhat below the supersymmetry breaking scale; (iii) the determinant of the quark mass matrix vanishes, and there is no strong $\mathrm{CP}$ problem; (iv) the superpotential has accidental B and L symmetries. The prediction ${m}_{\mathrm{up}}=0$ allows for an unambiguous test of the model at low energy.

Anomalous flavor [formula omitted]: predictive texture for bi-maximal neutrino mixing

We present a scenario which naturally provides bi-maximal neutrino mixings for a simultaneous explanation of the recent atmospheric and solar neutrino data. A crucial role is played by an anomalous flavor U(1) symmetry, which is also important for a natural understanding of charged fermion mass hierarchies and magnitudes of the CKM matrix elements. Within MSSM the solar neutrino problem can be resolved either through vacuum oscillations or the large mixing angle MSW solution. In supersymmetric GUTs such as SU(5) and SO(10) the MSW solution is realized. If the flavor U(1) also mediates supersymmetry breaking, the vacuum solution in MSSM is eliminated, and only the large mixing angle MSW solution survives.