Universal Seesaw Research Articles

Neutrino masses and mixings in a universal seesaw mass matrix model

Neutrino masses and mixings are investigated on the basis of a universal seesaw mass matrix model, in which quark (except for top) and charged lepton mass matrices M_f and neutrino mass matrix M_\nu are given by M_f \simeq m_L M_F^{-1} m_R and M_\nu \simeq m_L M_F^{-1} m_L^T (F=N), respectively. For a simple model which can successfully describe quark masses and mixings, we find that the observed neutrino data (except for the solar neutrino data) are favor to the intermediate mass scales O(m_R) = 10^{11} GeV and O(M_F)= 10^{13} GeV together with O(m_L)= 10^2 GeV. In spite of the largesse of O(m_R), the observed top quark mass can be consistently understood from the would-be seesaw mass matrix with these mass scales.

Predictive SUSY SO(10) model with very low tan β

The first fermion family might play a key role in understanding the structure of flavour: a role of the mass unification point. The GUT scale running masses m e,u,d are rather close, which may indicate an approximate symmetry limit. Following this observation, we present a new predictive approach based on the SUSY SO(10) theory with tan β ∼ 1. The inter-family hierarchy is first generated in a sector of hypothetical superheavy fermions and then transferred inversely to ordinary quarks and leptons by means of the universal seesaw mechanism. The Yukawa matrices are simply parametrized by the small complex coefficients ε u, d, e which are related by the SO(10) symmetry properties. Their values are determined by the ratio of the GUT scale M x ⋍ 10 16 GeV to a higher (possibly string) scale M ⋍ 10 17−10 18 GeV . The suggested ansatz correctly reproduces the fermion mass and mixing pattern. By taking as input the masses of leptons and c and b quarks, the ratio m s m d and the value of the Cabibbo angle, the u, d, s quark masses, top mass and tan β are computed. The top quark is naturally in the 100 GeV range, but obeys an upper limit M t < 165 GeV, while the lower bound M t > 160 GeV implies m s m d > 22 . tanβ can vary from 1.4 to 1.7. The proton decaying d = 5 operators qqql are naturally suppressed.

Quark mass hierarchies from the universal seesaw mechanism.

The paper is an extension of the previous work based on the idea of a universal seesaw mechanism to explain the hierarchies in the fermion mass spectrum. A model is proposed within the framework of left-right symmetry with a minimal Higgs system and an axial U(1) symmetry imposed to distinguish the generations. Previous work was confined, for mathematical simplifications, to the case of nonsingular mass matrices. In the present paper, singular matrices are considered. A systematic perturbative technique is developed to display the mass eigenvalues in terms of the vacuum expectation values of the assumed Higgs multiplets. The model successfully correlates the mass hierarchies among the quarks to the assumed hierarchies in the vacuum expectation values without appealing to a hierarchy in the Yukawa-type fermion-Higgs-boson couplings. By considering a general Higgs potential appropriate to the model, we study its minimization and prove that there exists an open subdomain in the parameter space where the orbit of the lowest minima of the potential corresponds to the kind of hierarchy in the vacuum expectation values needed for the success of the model.

Unified universal seesaw models.

A set of grand unified theories based upon the gauge groups SU(5)[sub [ital L]][times]SU(5)[sub [ital R]], SO(10)[sub [ital L]][times]SO(10)[sub [ital R]] and SU(4)[sub [ital C]][times]SU(4)[sub [ital L]][times]SU(4)[sub [ital R]] is explored. Several novel features distinguish these theories from the well-known SU(5), SO(10), and SU(4)[sub [ital C]][times]SU(2)[sub [ital L]][times]SU(2)[sub [ital R]] models which they generalize. Firstly, standard model quarks and leptons are accompanied by and mix with heavy SU(2)[sub [ital L]][times]SU(2)[sub [ital R]] singlet partners. The resulting fermion mass matrices are seesaw in form. Discrete parity symmetries render the determinants of these mass matrices real and eliminate [ital CP]-violating gauge terms. The unified seesaw models consequently provide a possible resolution to the strong [ital CP] problem. Secondly, sin[sup 2][theta][sub [ital W]] at the unification scale is numerically smaller than the experimentally measured [ital Z] scale value. The weak angle must therefore increase as it evolves down in energy. Finally, proton decay is suppressed by small seesaw mixing factors in all these theories.

Flavor Changing Neutral Currents in Universal Seesaw Model

Flavor Changing Neutral Currents in Universal Seesaw Model

Inverse hierarchy approach to fermion masses

The first fermion family might play a special role in understanding the physics of flavour. This possibility is suggested by the observation that the up-down splitting within quark families increases with the family number: m u d , m c > m s , m t ⪢ m b . We constrruct a model that realizes this feature of the spectrum in a natural way. The inter-family hierarchy is first generated by radiative phenomena in a sector of heavy isosinglet fermions and then transferred to quarks by means of a universal seesaw. A crucial role is played by left-right parity and up-down isotopic symmetry. No family symmetry is introduced. The model implies m u/ md > 0.5 and the Cabibbo angle is forced to be ∼√ m d / m s . The top quark is naturally in the 100 GeV range, but not too heavy: m t <150 GeV. Inspired by the mass matrices obtained in the model for quarks, we suggest an ansatz also including charged leptons. The difference between u-, d- and e-type fermions are simply parametrized by three complex coefficients ϵ u , ϵ d and ϵ e . Additional comnsistent predictions are obtained: m s = 100–150 MeV and m u / m d <0.75.

Flavor Changing Neutral Currents in Universal Seesaw Model

Flavor changing neutral currents (FCNC's) are investigated in the frame of the universal seesaw model with a left-right symmetric gauge group SU(4) cL × SU(4) cR × SU(2) L × SU(2) R × U(1)x. FCNC's at the tree level are induced through mixings between ordinary fermions and exotic fermions in this model. The FCNC contributions to the K L 0 → μ + m − transition and B 0 -B 0 mixing are compared with the experimental results and the predictions of the standard model. It is shown that FCNC's are safely suppressed and the universal seesaw mechanism works out without introducing the very small Yukawa coupling constants

Universal seesaw mechanisms for quark-lepton mass spectrum.

Problems of fermion mass hierarchies and generation mixings are investigated through universal seesaw mechanisms (USM's) in an extension of the standard model with a left-right-symmetric gauge group $\mathrm{SU}{(3)}_{c}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(2)}_{R}\ifmmode\times\else\texttimes\fi{}\mathrm{U}{(1)}_{y}$. Electroweak Higgs doublets and singlets induce USM's between ordinary fermion multiplets and exotic electroweak singlets of fermions. The USM's work singly in the charged-fermion sectors to suppress their masses below the electroweak mass scale, and doubly in the neutral-fermion sector to make neutrinos superlight. The wide gap between vanishingly small neutrino masses and the 100 GeV scale of the top-quark mass is explained by multiple USM suppressions without presuming a huge Majorana mass. A global chiral $\mathrm{U}{(1)}_{A}$ symmetry is introduced so as to circumvent the strong $\mathrm{CP}$ violation, to distinguish generations, and to restrict the pattern of the Yukawa interactions. Three kinds of electroweak Higgs singlets bring about USM's and cause the generation mixing leading to a realistic variety in each charge sector of the fermion mass spectrum. A fourth Higgs singlet with the largest vacuum expectation value is introduced to make the neutrino masses tiny and to make the axion invisible. By assigning chiral charges to make effective mass matrices of all fermion sectors of the extended Fritzsch type, characteristics of the mass spectra of charged fermions and the quark mixing matrix are described without introducing unnatural hierarchies in the Yukawa coupling constants. Neutrinos have a spectrum comprising doubly degenerate states with a smaller mass and a singlet state with a larger mass. The vacuum mixing angle takes a small value which is favorable for explaining both the new results of the GALLEX Collaboration and the data of the Homestake and Kamiokande experiments.

Exotic fermions in the left-right-symmetric model.

A systematic study is made of nonstandard fermion multiplets in left-right-symmetric models with the gauge group SU(3){sub {ital C}}{direct product}SU(2){sub {ital L}}{direct product}SU(2){sub {ital R}}{direct product}U(1){sub {ital B}{minus}{ital L}}. Constraints from gauge anomaly cancellation and invariance of Yukawa coupling terms are used to define interesting classes of exotic fermions. We identify the standard quark-lepton spectrum of left-right-symmetric models as the simplest member of an infinite class. The phenomenological implications of the next simplest member of this class are then studied. We also consider classes of exotic fermions which may couple to the standard fermions through doublet Higgs bosons. We then show that some of these exotics may be used to induce a generalized universal seesaw mechanism.

Matter-Induced Neutrino Oscillation in Double Universal Seesaw Model

The Mikheyev-Smirnov-Wolfenstein effect is investigated in an extended gauge field theory in which the universal seesaw mechanism is applied singly to the charged fermion sectors to lower their masses below the electroweak energy scale and doubly to the neutral fermion sector to make neutrinos superlight. At the first seesaw approximation, neutrinos are proved to have a distinctive spectrum consisting of doubly degenerate states with smaller mass mS and a singlet state with larger mas mL. The lepton mixing matrix is determined definitely in terms of the masses of charged leptons and down quarks, with a very small vacuum mixing angle sin θ= 0.043 ±0.004. The Schrödinger-like equation describing the spatial evolution of stationary neutrino flux is solved for globally-rotated-flavor wave functions. Comparison of its nonadiabatic solution with experimental results leads to an estimation mL2 - mS2 = (6 ±2) ×10-6 eV2 for the squared mass difference and a capture rate prediction of 74 ±12 SNU for the SAGE gallium experiment.

Matter-Induced Neutrino Oscillation in Double Universal Seesaw Model

The Mikheyev-Smirnov-Wolfenstein effect is investigated in an extended gauge field theory in which the universal seesaw mechanism is applied singly to the charged fermion sectors to lower their masses below the electroweak energy scale and doubly to the neutral fermion sector to make neutrinos superlight. At the first seesaw approximation, neutrinos are proved to have a distinctive spectrum consisting of doubly degenerate states with smaller mass ms and a singlet state with larger mass m L

Universal seesaw and radiative quark mass hierarchy

A new approach to the fermion mass problem is suggested. The mass hierarchy is first radiatively generated in a sector of heavy isosinglet fermions and then projected to the visible ones by means of a universal seesaw. In this way flavour-changing phenomena are naturally suppressed. A quantitatively correct picture of quark masses and mixing is obtained. In particular, in contrast to previous approaches, the correct value of the Cabibbo angle can be accommdated without troubles for the perturbation expansion. By fitting the values of the masses of the five known quarks, we find that the natural value of m t is in the 100 GeV range.

The mass-hierarchy puzzle and the 17 keV neutrino in the context of a Universal Seesaw Model

In the light of renewed evidence for the existence of a 17 keV neutrino, we study the possible mass patterns for the charged and the neutral leptons, in the context of a generalized “seesaw”-type of model, which implements a horizontal U(1) A Peccei-Quinn symmetry. Under some general assumptions concerning the structure of the mass matrix we find that the mass hierarchy between the first two generations of charged leptons and the third one is explained in terms of the natural scales of the model. At the same time, with the additional assumption of the proportionality of Majorana- and Dirac-type couplings, the spectrum of the neutral leptons contains two very light Majorana neutrinos, such as required by the MSW interpretation of the solar neutrino deficit, and the 17 keV “Simpson” neutrino. A cosmologically consistent decay mode of this neutrino is into a ν e and the axion.

Universal Seesaw Mechanism for Quarks and Leptons

Universal seesaw mechanism (USM) is implemented in a left-right symmetric unified theory of extended color and electroweak interactions to solve the problems of fermion mass hierarchies and generation mixings. The gauge group has the structure SU(4)cL ×SU(4)cR ×SU(2)L ×SU(2)R ×U(1)X in which the lepton number is treated as the fourth color and the U(1)X group is generated by a new charge X. Colored and non-colored Higgs fields induce USM between ordinary fermion multiplets and exotic electroweak singlets. USM is singly applied to the charged fermion sectors to suppress their average mass below the electroweak mass scale. On the other hand, USM applied doubly to the neutral fermion sector works to make neutrinos superlight. Prodigious gap between vanishingly small neutrino masses and the 102 GeV scale of the yet-undiscovered top quark is explained without presuming unnaturally huge mass scales. A global horizontal U(1)A symmetry is introduced so as to circumvent the strong CP violation and to restrict the Yukawa coupling constants. Colored Higgs quartets break the extended color symmetry SU(4)cL ×SU(4)cR down to SU(3)cL ×SU(3)cR by making the color interaction of lepton to be superweak. It is three kinds of colored Higgs bi-quartets which degrade the left-right symmetric color interaction into the conventional color interaction of vector type and play at the same time the roles to cause the USM and the generation mixing leading to a realistic variety in each sector of the fermion mass spectrum. Characteristics of mass spectra of charged fermions and the quark mixing matrix are described by adjusting the Yukawa coupling constants over a reasonable range of values.

Unification of forces and flavors for three families.

Electroweak, strong, and horizontal interactions are unified in a simple group with an anomaly-free representation which does not include mirror fermions or exotic quarks. \ifmmode\pm\else\textpm\fi{}1 charged, and neutral exotic leptons are needed in the model, but they acquire heavy masses as a consequence of the survival hypothesis, and also mix with the known leptons producing seesaw and universal seesaw mechanisms in a natural way. Masses for fermions in the third family arise at the tree level via a BCS (flavor-democracy) mass matrix. Masses for other known quarks and leptons can be generated by radiative corrections.

Three-generation seesaw model for quarks.

In the context of the universal seesaw mechanism,'' implemented in the framework of left-right-symmetric models, we discuss a particular scheme which allows the determination of the Kobayashi-Maskawa matrix elements in terms of the quark masses. By taking into account the experimental values of {ital V}{sub {ital u}{ital s}} and {ital V}{sub {ital c}{ital b}}, we obtain constraints on the strange- and the top-quark masses. After a brief discussion of the gauge-boson sector we also show that the flavor-changing neutral-current gauge interactions which arise in the model are safely suppressed and do not give rise to effects in conflict with the known experimental limits.

Quark masses and mixing angles from universal seesaw mechanism.

A universal seesaw mechanism is invoked to account for the observed fermion mass hierarchies. In the framework of left-right symmetry, heavy fermions (mass scale $\ensuremath{\chi}$) which are ${\mathrm{SU}(2)}_{L}\ensuremath{\bigotimes}{\mathrm{SU}(2)}_{R}$ singlets are postulated while retaining the simplest possible Higgs system: namely, ${\ensuremath{\varphi}(1,2,1)}_{+1}\ensuremath{\bigoplus}{\ensuremath{\varphi}(1,1,2)}_{+1}$ accompanied by a left-right singlet ${\ensuremath{\sigma}(1,1,1)}_{0}$ in the standard ${\mathrm{SU}(3)}_{C}\ensuremath{\bigotimes}{\mathrm{SU}(2)}_{L}\ensuremath{\bigotimes}{\mathrm{SU}(2)}_{R}\ifmmode\times\else\texttimes\fi{}{\mathrm{U}(1)}_{B\ensuremath{-}L}$ notation. Every conventional quark and lepton is accompanied by a nonmirror singlet heavy fermion, so that the associated mass matrix is doubled and has the seesaw form usually associated only with the neutrino mass matrix. In the single-generation case, the model provides a plausible explanation for the mass hierarchy ${m}_{e,u,d}\ensuremath{\sim}{10}^{\ensuremath{-}4}{M}_{W}$ and predicts ${m}_{{\ensuremath{\nu}}_{e}}{m}_{{\ensuremath{\nu}}_{R}}\ensuremath{\approx}{m}_{e}^{2}$, thus accounting for the superlightness of neutrinos. Combined with a U(1) axial symmetry, the mechanism provides a formalism in which the generations are distinguished and constraints emerge on the allowed form of mass matrices. In this paper, we consider the realistic case of three generations in a simplified version of the model in which $\mathrm{CP}$ violation does not arise from the gauge sector. Choosing the ${\mathrm{U}(1)}_{A}$ quantum numbers so that the mass matrices are of the Fritzsch type, we calculate experimentally measured Cabibbo-Kobayashi-Maskawa matrix elements ${V}_{\mathrm{us}}$, ${V}_{\mathrm{ub}}$, and ${V}_{\mathrm{cs}}$ and derive their dependence on quark mass parameters. An interesting correlation between ${V}_{\mathrm{us}}$ which measures the Cabibbo angle and ${V}_{\mathrm{ub}}$ which measures the charmless decay of the $b$ quark emerges from the model. ${V}_{\mathrm{ub}}$ is naturally suppressed if ${V}_{\mathrm{us}}=\sqrt{\frac{d}{s}}\ensuremath{-}\sqrt{\frac{u}{c}}$ to a very good approximation.

LIGHT FERMION MASSES FROM SU(3)color×U(1)e.m.?

We consider the hypothesis that (i) mv≃0 because the neutrino is SU (3)c× U (1) e.m. neutral, (ii) m electron = 0 at the isospin limit where mu=md, and (iii) all first-generation fer-mions turn massless as αc, α e.m. →0. This hypothesis is supported by the empirical Abraham-Lorentz-type mass formula m=(ζ1Q+ζ2B)2, whose quadratic structure is attributed to a universal seesaw mechanism. We demonstrate how such a formula can stay exact even when switching on the inter-generational mixings. We present a complete model with the above features which gives quark and lepton masses and the K-M matrix, including CP violation.

Family mass hierarchy from universal seesaw mechanism.

The ``universal seesaw mechanism,'' which accounts for ${\mathrm{m}}_{\mathrm{e}}$,u,d\ensuremath{\ll}${\mathrm{m}}_{\mathrm{W}}$, predicts ${\mathrm{m}}_{{\ensuremath{\nu}}_{\mathrm{L}}{\mathrm{m}}_{{\ensuremath{\nu}}_{\mathrm{R}}\mathrm{\ensuremath{\approxeq}}{\mathrm{m}}_{\mathrm{e}}^{2}}}$. Combined with an axial-vector symmetry principle, this mechanism allows for the coeexistence of heavy (\ensuremath{\lesssim}${\mathrm{m}}_{\mathrm{W}}$) families without appeal to a hierarchy in Yukawa couplings and without introduction of additional mass scales. It then follows that (i) the physical right-handed heavy (light) ordinary fermions are mostly SU(2${)}_{\mathrm{R}}$ singlets (doublets), (ii) there is no analogous neutrino mass hierarchy, and (iii) ${\mathrm{m}}_{\mathrm{PQ}{\mathrm{m}}_{{\ensuremath{\nu}}_{\mathrm{L}}\mathrm{\ensuremath{\approxeq}}{\mathrm{m}}_{\mathrm{W}}^{2}}}$ sets the Peccei-Quinn mass scale.

Universal seesaw mechanism?

The idea that fermions acquire their masses via a universal seesaw mechanism can provide a plausible explanation for the mass hier- archy ${\mathrm{m}}_{\mathrm{e}}$,u,d\ensuremath{\simeq}${10}^{\mathrm{\ensuremath{-}}4}$${\mathrm{M}}_{\mathrm{W}}$. A minimal SU(3${)}_{\mathrm{C}}$\ensuremath{\bigotimes}SU(2${)}_{\mathrm{L}}$ \ensuremath{\bigotimes}SU(2${)}_{\mathrm{R}}$\ensuremath{\bigotimes}U(1${)}_{\mathrm{B}\mathrm{\ensuremath{-}}\mathrm{L}}$ grand unifiable realization is presented. Whereas the fermionic representation is enlarged to include SU(2${)}_{\mathrm{L}}$\ensuremath{\bigotimes}SU(2${)}_{\mathrm{R}}$ singlets, the Higgs system contains none of the conventional scalars of left-right-symmetric models. An alternative way to account for the superlightness of neutrinos emerges.