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Large neutrino mixing angles in unified theories
Abstract
Typically in unified theories the neutrino mixing angles, like the
Cabibbo-Kobayashi-Maskawa (CKM) angles of the quarks, are related to the small
mass ratios between fermions of different generations and are therefore quite
small. A new approach for explaining the intergenerational mass hierarchies is
proposed here which, while giving small CKM angles, naturally leads to neutrino
angles of order unity. Such large mixing angles may be required for a
resolution of the atmospheric neutrino anomaly and may also be relevant for the
solar neutrino puzzle. The mechanism presented here provides a framework in
which novel approaches to the fermion mass question can arise. In particular,
within this framework a variant of the texture idea allows highly predictive
models to be constructed, an illustrative example of which is given. It is
shown how the neutrino mixing angles may be completely determined in such
schemes.
... In this paper we unify the anarchy hypothesis in the neutrino sector with the hierarchy observed in the quark and charged lepton sectors [20], [21], [22], [8] and analyze the resulting models from a probabilistic perspective. Such a unification is achieved in the framework of SU (5) grand unified theories, which treat quarks and leptons on similar footing. ...
... Our main analysis is focused on the Yukawa coupling structure obtained in SUSY SU (5) unified theories where the three families of 10 i fermions mix with vector-like fermions belonging to 10 α + 10 α representations that have GUT scale masses [20]. A variant of this model using the Froggatt-Nielsen mechanism [23], where the three families of 10 i fermions are distinguished by a flavor U (1) symmetry while the three families of 5 i are universal, is also analyzed allowing for effective non-renormalizable operators [8]. ...
... Our focus is the Yukawa couplings of the quarks and leptons in these theories. At the MSSM level, the Yukawa coupling matrices for the up quarks, down quarks, charged leptons, Dirac neutrinos and the right-handed Majorana neutrinos derived from these models will take the form [20]: ...
The masses of the charged fermion and the mixing angles among quarks are observed to be strongly hierarchical, while analogous parameters in the neutrino sector appear to be structure-less or anarchical. We develop a class of unified models based on SU(5) symmetry that explains these differing features probabilistically. With the aid of three input parameters that are hierarchical, and with the assumption that all the Yukawa couplings are uncorrelated random variables described by Gaussian distributions, we show by Monte Carlo simulations that the observed features of the entire fermion spectrum can be nicely reproduced. We extend our analysis to an SU(5)-based flavor U(1) model making use of the Froggatt-Nielsen mechanism where the order one Yukawa couplings are modeled as random variables, which also shows good agreement with observations.
... In this paper we unify the anarchy hypothesis in the neutrino sector with the hierarchy observed in the quark and charged lepton sectors [8,[19][20][21], and we analyze the resulting models from a probabilistic perspective. Such a unification is achieved in the framework of SUð5Þ grand unified theories, which treat quarks and leptons on similar footing. ...
... Our main analysis is focused on the Yukawa coupling structure obtained in supersymmetry (SUSY) SUð5Þ unified theories where the three families of 10 i fermions mix with vectorlike fermions belonging to 10 α þ 10 α representations that have grand unified theory (GUT) scale masses [19]. A variant of this model using the Froggatt-Nielsen mechanism [22], where the three families of 10 i fermions are distinguished by a flavor Uð1Þ symmetry while the three families of5 i are universal, is also analyzed allowing for effective nonrenormalizable operators [8]. ...
... Our focus is the Yukawa couplings of the quarks and leptons in these theories. At the MSSM level, the Yukawa coupling matrices for the up quarks, down quarks, charged leptons, Dirac neutrinos, and the righthanded Majorana neutrinos derived from these models will take the form [19] ...
The masses of the charged fermion and the mixing angles among quarks are observed to be strongly hierarchical, while analogous parameters in the neutrino sector appear to be structure-less or anarchical. We develop a class of unified models based on SU(5) symmetry that explains these differing features probabilistically. With the aid of three input parameters that are hierarchical, and with the assumption that all the Yukawa couplings are uncorrelated random variables described by Gaussian distributions, we show by Monte Carlo simulations that the observed features of the entire fermion spectrum can be nicely reproduced. We extend our analysis to an SU(5)-based flavor U(1) model making use of the Froggatt-Nielsen mechanism where the order one Yukawa couplings are modeled as random variables, which also shows good agreement with observations.
... Unification of the Standard Model (SM) gauge groups into a grand unified theory (GUT) [1][2][3] remains an attractive new-physics scenario: gUTs have the potential to (i) provide an explanation for the seemingly coincidental near-equality of SM gauge couplings at the high-energy scale M GUT ≈ 10 15 GeV, see e.g. [4,5]; (ii) (partially) explain the observed mass spectrum by unifying the fermionic representations [6][7][8]; (iii) account for neutrino masses [9][10][11][12][13] with a suitable see-saw mechanism [14][15][16]; and (iv) offer a scenario for leptogenesis, see e.g. [17][18][19][20]. ...
... (D. 12) We note that the normalisation of the various operators is arbitrary and that the six quartic couplings λ i were defined such that perturbativity is lost around λ i 1. Our notation and conventions translate to those of [54,55,85] according to: (D.14) 29 Note that this global symmetry could be restored for τ1 = 0 by complexifying and assigning a U(1) ...
A bstract
Grand unification of gauge couplings and fermionic representations remains an appealing proposal to explain the seemingly coincidental structure of the Standard Model. However, to realise the Standard Model at low energies, the unified symmetry group has to be partially broken by a suitable scalar potential in just the right way. The scalar potential contains several couplings, whose values dictate the residual symmetry at a global minimum. Some (and possibly many) of the corresponding symmetry-breaking patterns are incompatible with the Standard Model and therefore non-admissible.
Here, we initiate a systematic study of radiative symmetry breaking to thereby constrain viable initial conditions for the scalar couplings, for instance, at the Planck scale. We combine these new constraints on an admissible scalar potential with well-known constraints in the gauge-Yukawa sector into a general blueprint that carves out the viable effective-field-theory parameter space of any underlying theory of quantum gravity.
We exemplify the constraining power of our blueprint within a non-supersymmetric SO(10) GUT containing a 16 H - and a 45 H -dimensional scalar representation. We explicitly demonstrate that the requirement of successful radiative symmetry breaking to the correct subgroups significantly constraints the underlying microscopic dynamics. The presence of non-admissible radiative minima can even entirely exclude specific breaking chains: in the SO(10) example, Pati-Salam breaking chains cannot be realised since the respective minima are never the deepest ones.
... Unification of the Standard Model (SM) gauge groups into a grand unified theory (GUT) [1][2][3] remains an attractive new-physics scenario: GUTs have the potential to (i) provide an explanation for the seemingly coincidental near-equality of SM gauge couplings at the high-energy scale M GUT ≈ 10 15 GeV, see e.g. [4,5]; (ii) (partially) explain the observed mass spectrum by unifying the fermionic representations [6][7][8]; (iii) account for neutrino masses [9][10][11][12][13] with a suitable see-saw mechanism [14][15][16]; and (iv) offer a scenario for leptogenesis, see e.g. [17][18][19][20]. ...
... (D. 12) We note that the normalisation of the various operators is arbitrary and that the six quartic couplings λ i were defined such that perturbativity is lost around λ i 1. Our notation and conventions translate to those of [53,54,80] according to: E β-functions ...
Grand unification of gauge couplings and fermionic representations remains an appealing proposal to explain the seemingly coincidental structure of the Standard Model. However, to realise the Standard Model at low energies, the unified symmetry group has to be partially broken by a suitable scalar potential in just the right way. The scalar potential contains several couplings, whose values dictate the residual symmetry at a global minimum. Some (and possibly many) of the corresponding symmetry-breaking patterns are incompatible with the Standard Model and therefore non-admissible. Here, we initiate a systematic study of radiative symmetry breaking to thereby constrain viable initial conditions for the scalar couplings, for instance, at the Planck scale. We combine these new constraints on an admissible scalar potential with well-known constraints in the gauge-Yukawa sector into a general blueprint that carves out the viable effective-field-theory parameter space of any underlying theory of quantum gravity. We exemplify the constraining power of our blueprint within a non-supersymmetric GUT containing a - and a -dimensional scalar representation. We explicitly demonstrate that the requirement of successful radiative symmetry breaking to the correct subgroups significantly constraints the underlying microscopic dynamics. The presence of non-admissible radiative minima can even entirely exclude specific breaking chains: In the example, Pati-Salam breaking chains cannot be realised since the respective minima are never the deepest ones.
... For previous works on correcting fermion mass relation by employing vectorlike states, see, e.g., Refs. [61][62][63][64][65][66][67][68][69][70][71][72][73]. ...
Embedding inflation within a grand unified theory is an intriguing idea towards a more fundamental understanding of particle physics and cosmology. However, within the framework of supersymmetric S U ( 5 ) grand unified theory inflation, models typically feature light color octets and weak triplets that ruin the successful gauge coupling unification of the mimimal supersymmetric Standard Model. We present a new possibility for naturally splitting the electronlike states from the colored ones within vectorlike 10-plets by utilizing their couplings with 40-plets that lack electronlike states. Together with the extra light weak doublets from the double missing partner mechanism, the appearance of the light electronlike states from our proposed generalized missing partner mechanism restores gauge coupling unification. Remarkably, the same vectorlike 10-plets cure the bad mass relations between the down quarks and the charged leptons. Discovering the light relic states at future colliders would provide a “smoking gun” signal of the scenario.
Published by the American Physical Society 2024
... Understanding the pattern of fermion masses and mixings presents a two-fold puzzle for particle physics. While some success has been achieved towards predicting fermion mixings through the imposition of family symmetries [4][5][6][7][8], less progress has been made concerning the formulation of a fully convincing theory of fermion mass hierarchies, though there have been many proposals in this direction [9][10][11][12][13][14][15][16][17][18]. ...
A bstract
The so-called Golden Mass Relation provides a testable correlation between charged-lepton and down-type quark masses, that arises in certain flavor models that do not rely on Grand Unification. Such models typically involve broken family symmetries. In this work, we demonstrate that realistic fermion mass relations can emerge naturally in modular invariant models, without relying on ad hoc flavon alignments. We provide a model-independent derivation of a class of mass relations that are experimentally testable. These relations are determined by both the Clebsch-Gordan coefficients of the specific finite modular group and the expansion coefficients of its modular forms, thus offering potential probes of modular invariant models. As a detailed example, we present a set of viable mass relations based on the Γ 4 ≅ S 4 symmetry, which have calculable deviations from the usual Golden Mass Relation.
... For previous works on correcting fermion mass relation by employing vectorlike states, see, e.g., Refs. [60][61][62][63][64][65][66][67][68][69][70][71][72]. ...
We generalise the Missing Partner Mechanism to split the electron-like states from the coloured ones of vectorlike SU(5) 10-plets without fine-tuning. Together with the extra light weak doublets from the Double Missing Partner Mechanism (DMPM), this realises gauge coupling unification in the presence of a light weak triplet and colour octet, the characteristic light relics from the adjoint in SU(5) GUT Inflation models. Additionally, we show how the vectorlike 10-plets may generate realistic fermion masses while the DMPM ensures that dimension five nucleon decay is suppressed. A discovery of the light relic states at future colliders would provide a "smoking gun" signal of the scenario.
... This gauge symmetry generates textures that produce flavor changes in the neutral currents and that, in principle, could be seen in future colliders. There are models with electroweak extensions of the SM such as SO (14), SU (9), 3-3-1, U (1) X , etc. [82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97] that attempt to explain the flavor and the mass hierarchy problem of the SM. Another mechanism to generate textures in the Yukawa Lagrangian is through additional discrete or global symmetries. ...
A model with fermion and scalar fields charged under a Peccei–Queen (PQ) symmetry is proposed. The PQ charges are chosen in such a way that they can reproduce mass matrices with five texture zeros, which can generate the fermion masses, the CKM matrix, and the PMNS matrix of the Standard Model (SM). To obtain this result, at least 4 Higgs doublets are needed. As we will see in the manuscript this is a highly non-trivial result since the texture zeros of the mass matrices impose a large number of restrictions. This model shows a route to understand the different scales of the SM by extending it with a multi-Higgs sector and an additional PQ symmetry. Since the PQ charges are not universal, the model predicts flavor-changing neutral currents (FCNC) at the tree level, a feature that constitutes the main source of restrictions on the parameter space. We report the allowed regions by lepton decays and compare them with those coming from the semileptonic decays K ± ⟶ π ν ¯ ν . We also show the excluded regions and the projected bounds of future experiments for the axion–photon coupling as a function of the axion mass and compare it with the parameter space of our model.
... Here each entry in the matrices has an order one Yukawa coupling coefficient which is not explicitly shown. These matrices, which are modifications of the lop-sided matrices proposed in the context of SU(5) unified theory to explain simultaneously the small CKM mixing angles and the large neutrino mixing angles [38][39][40], can provide a good understanding of several intricate features of the fermion mass and mixing pattern. The masses obey the following hierarchy: ...
A bstract
We investigate the phenomenology of a non-thermal dark matter (DM) candidate in the context of flavor models that explain the hierarchy in the masses and mixings of quarks and leptons via the Froggatt-Nielsen (FN) mechanism. A flavor-dependent U(1) FN symmetry explains the fermion mass and mixing hierarchy, and also provides a mechanism for suppressed interactions of the DM, assumed to be a Majorana fermion, with the Standard Model (SM) particles, resulting in its FIMP (feebly interacting massive particle) character. Such feeble interactions are mediated by a flavon field through higher dimensional operators governed by the U(1) FN charges. We point out a natural stabilizing mechanism for the DM within this framework with the choice of half-integer U(1) FN charge n for the DM fermion, along with integer charges for the SM fermions and the flavon field. In this flavon portal scenario, the DM is non-thermally produced from the decay of the flavon in the early universe which becomes a relic through the freeze-in mechanism. We explore the allowed parameter space for this DM candidate from relic abundance by solving the relevant Boltzmann equations. We find that reproducing the correct relic density requires the DM mass to be in the range (100 − 300) keV for n = 7 . 5 and (3 − 10) MeV for n = 8 . 5 where n is the U(1) FN charge of the DM fermion.
... Here each entry in the matrices has an order one Yukawa coupling coefficient which is not explicitly shown. These matrices, which are modifications of the lop-sided matrices proposed in the context of SU (5) unified theory to explain simultaneously the small CKM mixing angles and the large neutrino mixing angles [35][36][37], can provide a good understanding of several intricate features of the fermion mass and mixing pattern. The masses obey the following hierarchy: ...
We investigate the phenomenology of a non-thermal dark matter (DM) candidate in the context of flavor models that explain the hierarchy in the masses and mixings of quarks and leptons via the Froggatt-Nielsen (FN) mechanism. A flavor-dependent symmetry explains the fermion mass and mixing hierarchy, and also provides a mechanism for suppressed interactions of the DM, assumed to be a Majorana fermion, with the Standard Model (SM) particles, resulting in its FIMP (feebly interacting massive particle) character. Such feeble interactions are mediated by a flavon field through higher dimensional operators governed by the charges. We point out a natural stabilizing mechanism for the DM within this framework with the choice of half-integer charge n for the DM fermion, along with integer charges for the SM fermions and the flavon field. In this flavon portal scenario, the DM is non-thermally produced from the decay of the flavon in the early universe which becomes a relic through the freeze-in mechanism. We explore the allowed parameter space for this DM candidate from relic abundance by solving the relevant Boltzmann equations. We find that reproducing the correct relic density requires the DM mass to be in the range keV for n=7.5 and MeV for n=8.5 where n is the charge of the DM fermion.
... This gauge symmetry generates textures that produce flavor changes in the neutral currents and that, in principle, could be seen in future colliders. There are models with electroweak extensions of the SM such as SO (14), SU (9), 3-3-1, U (1) X , etc. [88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103] that attempt to explain the flavor and the mass hierarchy problem of the SM. Another mechanism to generate textures in the Yukawa Lagrangian is through additional discrete or global symmetries. ...
A model with fermion and scalar fields charged under a Peccei-Queen~(PQ) symmetry is proposed. The PQ charges are chosen in such a way that they can reproduce mass matrices with five texture zeros, {which can generate} the fermion masses, the CKM matrix, and the PMNS matrix of the Standard Model~(SM). To obtain this result, at least 4~Higgs doublets are needed. As we will see in the manuscript this is a highly non-trivial result since the texture zeros of the mass matrices impose a large number of restrictions. This model shows a route to understand the different scales of the SM by extending it with a multi-Higgs sector and an additional PQ symmetry. Since the PQ charges are not universal, the model presents flavor-changing neutral currents~(FCNC) at the tree level, a feature that constitutes the main source of restrictions on the parameter space. We report the allowed regions by lepton decays and compare them with those coming from the semileptonic decays . We also show the excluded regions and the projected bounds of future experiments for the axion-photon coupling as a function of the axion mass and compare it with the parameter space of our model.
... For alternative attempts to explain the flavor puzzle utilizing vectorlike fermions see Refs.[60][61][62][63][64]. ...
The clockwork mechanism, which can naturally explain the origin of small numbers, is implemented in SO(10) grand unified theories to address the origin of hierarchies in fermion masses and mixings. We show that a minimal Yukawa sector involving a 10H and 126¯H of Higgs bosons, extended with two clockwork chains consisting of 16+16¯ vectorlike fermions, can explain the hierarchical patterns with all the Yukawa couplings being of order one. Emergence of a realistic mass spectrum does not require any symmetry that distinguishes the three generations. We develop clockwork-extended SO(10) GUTs both in the context of SUSY and non-SUSY frameworks. Implementation of the mechanism in non-SUSY scenario assumes a Peccei-Quinn symmetry realized at an intermediate scale, with the clockwork sector carrying nontrivial charges, which solves the strong CP problem and provides axion as a dark matter candidate.
... Vector-like fermions are used to generate small quark masses through a see-saw type mechanism [40][41][42][43] and radiative corrections [44]. The flavor structure has been studied in unified theories with vectorlike fermions [45][46][47][48][49][50][51][52]. It would be meaningful to reexamine various models with our conclusions in mind. ...
We propose a bottom-up approach in which a structure of high-energy physics is explored by accumulating existence proofs and/or no-go theorems in the standard model or its extension. As an illustration, we study fermion mass hierarchies based on an extension of the standard model with vector-like fermions. It is shown that the magnitude of elements of Yukawa coupling matrices can become O(1) and a Yukawa coupling unification can be realized in a theory beyond the extended model, if vector-like fermions mix with three families. In this case, small Yukawa couplings in the standard model can be highly sensitive to a small variation of matrix elements, and it seems that the mass hierarchy occurs as a result of fine tuning.
... We present a modified ansatz for the Yukawa couplings of Higgs doublet Φ a , where Y ij are order one coefficients, m i stands for the mass of fermion i and v 246 GeV is the electroweak vacuum expectation value (VEV). Our modified ansatz can be realized in the context of unification [17]. We refer to the 2HDM with no additional symmetry as simply the two Higgs doublet model (2HDM), with no qualifier, as opposed to type-I or type-II models, which require additional assumptions. ...
A bstract
We show that the rate for di-Higgs production at the LHC can be enhanced by a factor as large as 25 compared to the Standard Model value in the two Higgs doublet model, while being consistent with the known properties of the observed Higgs boson h . There are correlated modifications in t t ¯ h and resonant Zh production rates, which can serve as tests of this model. Our framework treats both Higgs doublets on equal footing, each with comparable Yukawa couplings to fermions. The Cheng-Sher ansatz for multi-Higgs doublet model is shown to be strongly disfavored by current experiments. We propose a new ansatz for the Yukawa couplings of the Higgs doublets Φ a is proposed, where Y ij ( a ) = C ij ( a ) · min{ m i , m j }/ v , with C ij ( a ) being order one coefficients, m i the mass of fermion i and v the electroweak vacuum expectation value. Such a pattern of couplings can explain the observed features of fermion masses and mixings and satisfies all flavor violation constraints arising from the exchange of neutral Higgs bosons. The rate for μ → eγ decay and new contributions to CP violation in B s − B ¯ s mixing are predicted to be close to the experimental limits.
A flavor-dependent model (FDM) is proposed in this work. The model extends the Standard Model by an extra U ( 1 ) F local gauge group, two scalar doublets, one scalar singlet and two right-handed neutrinos, where the additional U ( 1 ) F charges are related to the particles’ flavor. The new fermion sector in the FDM can explain the flavor mixings puzzle and the mass hierarchy puzzle simultaneously, and the nonzero Majorana neutrino masses can be obtained naturally by the Type I see-saw mechanism. In addition, the B meson rare decay processes B ¯ → X s γ , B s 0 → μ + μ - , the top quark rare decay processes t → c h , t → u h and the τ lepton flavor violation processes τ → 3 e , τ → 3 μ , μ → 3 e predicted in the FDM are analyzed.
A Peccei-Quinn (PQ) symmetry is proposed, in order to generate in the Standard Model (SM) quark sector a realistic mass matrix ansatz with five texture-zeros. Limiting our analysis to Hermitian mass matrices we show that this requires a minimum of 4 Higgs doublets. This model allows assigning values close to 1 for several Yukawa couplings, giving insight into the origin of the mass scales in the SM. Since the PQ charges are non-universal the model features Flavor-Changing Neutral Currents (FCNC) at the tree level. From the analytical expressions for the FCNC we report the allowed region in the parameter space obtained from the measurements of branching ratios of semileptonic meson decays.
We review theoretical ideas, problems and implications of neutrino masses and mixing angles. We give a general discussion of schemes with three light neutrinos. Several specific examples are analysed in some detail, particularly those that can be embedded into grand unified theories.
A Peccei-Quinn~(PQ) symmetry is proposed, in order to generate in the Standard Model~(SM) quark sector a realistic mass matrix ansatz with five texture-zeros. Limiting our analysis to Hermitian mass matrices we show that this requires a minimum of 4 Higgs doublets. This model allows assigning values close to 1 for several Yukawa couplings, giving insight into the origin of the mass scales in the SM. Since the PQ charges are non-universal the model features Flavor-Changing Neutral Currents~(FCNC) at the tree level. We calculate the FCNC couplings of the most general low-energy effective Lagrangian for the axion in a procedure valid for an arbitrary number of Higgs doublets. Finally, we report the allowed region in the parameter space obtained from the measurements of branching ratios of semileptonic meson decays.
Most of the free parameters in the Standard Model (SM) — a quantum field theory which has successfully elucidated the behaviors of strong, weak and electromagnetic interactions of all the known fundamental particles, come from the lepton and quark flavors. The discovery of neutrino oscillations has proved that the SM is incomplete, at least in its lepton sector; and thus the door of opportunity is opened to exploring new physics beyond the SM and solving a number of flavor puzzles. In this review article we give an overview of important progress made in understanding the mass spectra, flavor mixing patterns, CP-violating effects and underlying flavor structures of charged leptons, neutrinos and quarks in the past twenty years. After introducing the standard pictures of fermion mass generation, flavor mixing and CP violation in the SM extended with the presence of massive Dirac or Majorana neutrinos, we briefly summarize current experimental knowledge about the flavor parameters of quarks and leptons. Various ways of describing flavor mixing and CP violation are discussed, the renormalization-group evolution of flavor parameters is illuminated, and the matter effects on neutrino oscillations are interpreted. Taking account of possible extra neutrino species, we propose a standard parametrization of the 6 × 6 flavor mixing matrix and comment on the phenomenological aspects of heavy, keV-scale and light sterile neutrinos. We pay particular attention to those novel and essentially model-independent ideas or approaches regarding how to determine the Yukawa textures of Dirac fermions and the effective mass matrix of Majorana neutrinos, including simple discrete and continuous flavor symmetries. An outlook to the future development in unraveling the mysteries of flavor structures is also given.
We construct a model which provides maximal mixing between a pseudo-Dirac nu (mu)/nu (tau) pair, based on a local U(1)L-mu-L-tau symmetry. Its strengths, weaknesses and phenomenological consequences are examined. The mass gap necessitated by the pseudo-Dirac structure is most naturally associated with the LSND anomaly. The solar neutrino problem then requires a light mirror or sterile neutrino. By paying a fine-tuning price to nullify the mass gap, one can also invoke nu (e)-->nu (mu,tau) for the solar problem. The model predicts a new intermediate range force mediated by the light gauge boson of U(1)(L mu -L tau). Through the mixing of mu, tau and e, this force couples to electrons and thus may be searched for in precision "gravity" experiments.
In a model proposed in 2012, all flavor mixing has a single source and is
governed by a single "master matrix." This model was shown to give several
predictions for quark and lepton masses and mixing angles and for mixing angles
within SU(5) multiplets that are observable in proton decay. Here it is shown
that the same master matrix controls the flavor-changing processes mediated by
a singlet scalar that exists in the model, giving predictions for tau to mu +
gamma, tau to e + gamma, and mu to e + gamma.
Recently, various phenomenological implications of the existence of extra space-time dimensions have been investigated. In this letter, we construct a model with realistic fermion mass hierarchy with (large) extra dimensions beyond the usual four dimensions. In this model, it is assumed that some matter fields live in the bulk and the others are confined to our four-dimensional wall. It can naturally reproduce the quark and lepton mass hierarchy and mixing angles without any symmetry arguments. We also discuss some possibilities of obtaining suitable neutrino masses and mixings for the solar and atmospheric neutrino problems.
We show that judiciously chosen R-parity violating terms in the minimal
renormalizable supersymmetric SU(5) are able to correct all the
phenomenologically wrong mass relations between down quarks and charged
leptons. The model can accommodate neutrino masses as well. One of the most
striking consequences is a large mixing between the electron and the Higgsino.
We show that this can still be in accord with data in some regions of the
parameter space and possibly falsified in future experiments.
The current status of the physics of massive neutrinos is reviewed with a forward-looking emphasis. The article begins with the general phenomenology of neutrino oscillations in vacuum and matter and documents the experimental evidence for oscillations of solar, reactor, atmospheric and accelerator neutrinos. Both active and sterile oscillation possibilities are considered. The impact of cosmology (BBN, CMB, leptogenesis) and astrophysics (supernovae, highest energy cosmic rays) on neutrino observables and vice versa, is evaluated. The predictions of grand unified, radiative and other models of neutrino mass are discussed. Ways of determining the unknown parameters of three-neutrino oscillations are assessed, taking into account eight-fold degeneracies in parameters that yield the same oscillation probabilities, as well as ways to determine the absolute neutrino mass scale (from beta-decay, neutrinoless double-beta decay, large scale structure and Z-bursts). Critical unknowns at present are the amplitude of νμ→νe oscillations and the hierarchy of the neutrino mass spectrum; the detection of CP violation in the neutrino sector depends on these and on an unknown phase. The estimated neutrino parameter sensitivities at future facilities (reactors, superbeams, neutrino factories) are given. The overall agenda of a future neutrino physics program to construct a bottom-up understanding of the lepton sector is presented.
Recently, various phenomenological implications of the existence of extra space–time dimensions have been investigated. In this letter, we construct a model with realistic fermion mass hierarchy with (large) extra dimensions beyond the usual four dimensions. In this model, it is assumed that some matter fields live in the bulk and the others are confined to our four-dimensional wall. It can naturally reproduce the quark and lepton mass hierarchy and mixing angles without any symmetry arguments. We also discuss some possibilities of obtaining suitable neutrino masses and mixings for the solar and atmospheric neutrino problems.
A brief review is given of some ideas for explaining neutrino masses and mixings within the context of supersymmetric grand unification. Emphasis is put on so-called lopsided models.
On the basis of a seesaw-type mass matrix model for quarks and leptons, where mL∝mR are universal for f=u, d, v and e (up-quark, downquark, neutrino and charged lepton sectors respectively), and MF has a form [(unit matrix)+(democratic-type matrix)], neutrino masses and mixings are investigated. We try to understand a large vµ−vτ mixing, i.e. sin2 2θ23~1, with mv1 ≪ mv2~mv3, which has been suggested by the atmospheric neutrino data.
We show that the sizable D-term contributions to the sfermion mass spectrum can be signatures of a certain grand unified theory (GUT), GUT. Note that these D-term contributions destroy the degeneracy of sfermion masses among different generations in this model. This is different
from previous works, which have argued for the D-term contributions, which destroy the degeneracy of masses only between sfermions with different quantum charges, as a signature
of GUT with a larger rank unification group. Such D-terms are strongly constrained by the flavor-changing neutral current processes if the SUSY breaking scale is the weak scale.
However, in , a natural SUSY-type sfermion mass spectrum is obtained, and if the masses of sfermions are larger than to realize the 126 GeV Higgs and the other sfermion masses are , then a sizable D-term contribution is allowed. If these D-terms can be observed in future experiments, like the 100 TeV proton collider or muon collider, we may confirm the GUT.
The Standard Model fermion sector is enlarged by either one light singlet vector-like down-type quark or one light vector-like lepton doublet, which might be accommodated within a five-dimensional representation of SU(5). At low energies the inclusion of these states affects precisely measured observables in flavor physics, as well as electroweak precision measurements. These experimental results strongly constrain couplings of vector-like states to the Standard Model particles. Having these bounds, we investigate the impact of vector-like fermions on the mass matrices for down-type quarks and charged leptons in an SU(5) setting. We find that unitary transformations relating an arbitrary flavor basis to the mass eigenstate basis depend only on three free parameters. Then we discuss the parameter space constrained by low-energy data assuming vector-like quark and vector-like lepton masses to be 800 GeV and 400 GeV, respectively. We demonstrate that these two scenarios generate unique patterns for relevant proton decay widths. A further improvement of experimental bounds on proton decay modes would thus differentiate the allowed parameter space. We finally present two full-fledged SU(5) models that allow for gauge coupling unification with light vector-like fermions under consideration and discuss their viability.
In the previous paper, we have shown that and
can identify the grand unification group SU(5), SO(10), or
in typical anomalous supersymmetric (SUSY) grand unified theory (GUT)
in which nucleon decay via dimension-6 operators becomes dominant. When the grand unification group is not SU(5), while when the grand
unification group is . Moreover, is implied. Main
ambiguities come from the diagonalizing matrices for quark and lepton mass
matrices in this calculation once we fix the vacuum expectation values of GUT
Higgs bosons. In this paper, we calculate and in SUSY GUT with anomalous gauge symmetry, in which realistic
quark and lepton masses and mixings can be obtained though the flavor symmetry
constrains Yukawa couplings at the GUT scale. The ambiguities of
Yukawa couplings are expected to be reduced. We show that the predicted region
for and is more restricted than in the model without
as expected. Moreover, we re-examine the previous claim for the
identification of grand unification group with 100 times more model points
( model points), including model.
Strictly adhering to the standard supersymmetric seesaw mechanism, we present a neutrino mass model which allows successful standard thermal leptogenesis compatible with gravitino cosmology. Some neutrino Yukawa couplings are naturally much larger than the naive estimates following from the seesaw formula. This leads to large BR(mu -> e gamma), detectable in the next round of experiments. Ratios of mu -> e gamma, tau -> ey and tau -> mu gamma branching ratios are predicted in terms of the measurable neutrino mass matrix. (c) 2005 Elsevier B.V. All rights reserved.
It is proposed that all flavor mixing is caused by the mixing of the three quark and lepton families with vectorlike fermions in 5 +
5
multiplets of
SU
(5). The entire 3 × 3 complex mass matrix of the neutrinos
M
ν is then found to have a simple expression in terms of two complex parameters and an overall scale. Thus, all the presently unknown neutrino parameters are predicted. The best fits are for θ
atm
≲ 40° The leptonic
Dirac CP phase is found to be somewhat greater than π.
It is shown that the minimal renormalizable supersymmetric SU(5) grand
unified theory can be made realistic by the inclusion of a single
vectorlike 5 + 5 pair. Such a modification can at the same time correct
the usual bad mass relations for the first two generations and safely
increase the nucleon lifetime. The model predicts the lifetime of at
least some decay rate to be less than approximately 1034 yrs, provided
that all the superpartners of the minimal supersymmetric standard model
lie below 3 TeV. The two statements will be tested by the next proton
decay measurements and LHC, respectively.
We investigate the effects of messenger–matter mixing on the lightest CP–even Higgs boson mass mh in gauge–mediated supersymmetry breaking models. It is shown that with such mixings mh can be raised to about 125 GeV, even when the superparticles have sub–TeV masses, and when the gravitino has a cosmologically preferred sub-keV mass. In minimal gauge mediation without messenger-matter mixing, realizing mh∼125 GeV would require multi-TeV supersymmetry spectrum. The increase in mh due to messenger–matter mixing is maximal in the case of messengers belonging to 10+10̅ of SU(5) unification, while it is still significant when they belong to 5+5̅ of SU(5). Our results are compatible with gauge coupling unification, perturbativity, and the unification of messenger Yukawa couplings. We embed these models into a grand unification framework with a U(1) flavor symmetry that addresses the fermion mass hierarchy and generates naturally large neutrino mixing angles. While supersymmetry mediated flavor changing processes are sufficiently suppressed in such an embedding, small new contributions to K0-K0̅ mixing can resolve the apparent discrepancy in the CP asymmetry parameters sin2β and ϵK.
In the SUSY SO(10) GUT context, we study the exclusive processes
. Using the Wilson coefficients of the relevant operators including the new operators
which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like the invariant mass spectrum (IMS), lepton pair forward-backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients
, among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA,
, and
of
decay, which are expected to be measured in B factories, the deviation of
in
can reach 0.1 from SM, which could be seen in B factories, and the average of the normal polarization
can reach several percent for
and it is 0.05 or so for
, which could be measured in the future super B factories and provide useful information to probe new physics and discriminate different models.
A Higgs-like particle with mass of order 125 GeV has been observed by both ATLAS and CMS experiments. This Higgs mass causes sparticle masses in the several to multi-TeV range in the simple version of minimal GMSB models. We consider the effects of messenger–matter mixing on the lightest CP–even Higgs boson mass in gauge–mediated supersymmetry breaking models. We find with such mixings a 125 GeV Higgs boson can be naturally obtained even with a sub–TeV SUSY spectrum, and when the gravitino has a cosmologically preferred sub–keV mass. In addition, when these models are embedded into a grand unification framework with a U(1)U(1) flavor symmetry they explain the fermion mass hierarchy and generate naturally large neutrino mixing angles accompanied with small quark mixing angles. While SUSY mediated flavor changing processes are sufficiently suppressed in such an embedding, it can resolve the apparent discrepancy in the CP asymmetry parameters sin2β and ϵKϵK, and it predicts an observable μ→eγμ→eγ decay rate.
Assuming Majorana neutrinos, we infer from oscillation data the expected values of the parameters mνe and mee probed by β and 0ν2β-decay experiments. If neutrinos have a ‘normal hierarchy’ we get the 90% CL range |mee|=(0.7−4.6) meV, and discuss in which cases future experiments can test this possibility. For ‘inverse hierarchy’, we get |mee|=(12−57) meV and mνe=(40−57) meV. The 0ν2β data imply that almost degenerate neutrinos are lighter than 1.05h eV at 90% CL (h∼1 parameterizes nuclear uncertainties), competitive with the β-decay bound. We critically reanalyse the data that were recently used to claim an evidence for 0ν2β, and discuss their implications. Finally, we review the predictions of flavour models for mee and θ13.
A structure is proposed for the mass matrices of the quarks and leptons that arises in a natural way from the assumption that the breaking of SO(10) gauge symmetry is achieved by the smallest possible set of vacuum expectation values. This structure explains well many features of the observed spectrum of quarks and leptons. It reproduces the Georgi-Jarlskog mass relations and leads to a charm quark mass in reasonable agreement with data. It also predicts a large mixing angle between {nu}{sub {mu}} and {nu}{sub {tau}} , as suggested by atmospheric neutrino data. The mixing angles of the electron neutrino are predicted to be small. {copyright} {ital 1998} {ital The American Physical Society}
It is shown that SO(10) grand unified models of quark and lepton masses that are of a simple and well‐motivated type lead to a relation between the Dirac
CP violating phase in the leption sector and the neutrino mixing angle
θ
13
.
The main assumptions are that SO(10) is the unified symmetry, that the mass matrices have the “lopsided form, and that the neutrino
Dirac mass matrix, like the up quark mass matrix, has a very small first row and column.
We study the BâÏK{sub S} decay in a supersymmetric (SUSY) SO(10) grand unified theory (GUT). We calculate the mass spectrum of sparticles for a given set of parameters at the grand unified theory (GUT) scale. We complete the calculations of the Wilson coefficients of operators including the new operators which are induced by neutral Higgs boson (NHB) penguins at LO using the mass insertion approximation (MIA) with double insertions. It is shown that the recent experimental results on the time-dependent CP asymmetry S{sub Ï}{sub K} in BâÏK{sub S}, which is negative and cannot be explained in the standard model (SM), can be explained in the model where there are flavor nondiagonal right-handed down squark mass matrix elements of second and third generations whose size satisfies all relevant constraints from known experiments (Ïâμγ, BâX{sub S}γ, B{sub s}âμ{sup +}μâ», BâX{sub s}μ{sup +}μâ», BâX{sub s}g, δM{sub s}, etc.). At the same time, the branching ratio for the decay can also be in agreement with experimental measurements.
We present a short discussion on the expected magnitude of |Ue3| in the context of various scenarios proposed to describe the neutrino masses and mixing. Generic expectation is relatively large (> 0.05) values for |Ue3| which occur in many well-motivated theoretical scenarios and models.
It was recently proposed that all flavor mixing has a single source, namely
the mixing of the three quark and lepton families with "extra" vectorlike
fermions in 5 + 5-bar multiplets of SU(5). This was shown to lead to several
testable predictions including neutrino masses and CP-violating phases. Here it
is shown that the mixing angles within grand unified fermion multiplets are
also predicted. Proton decay branching ratios would thus give several
independent tests of the model. Certain model parameters could be determined
independently from the quark and lepton spectrum and from proton decay.
The weak decays of Lambdab-->Lambdal+l- (l=e, mu) are investigated in the minimal supersymmetric standard model (MSSM) and also in supersymmetric (SUSY) SO(10) grand unified models. In the MSSM special attention is paid to the neutral Higgs bosons (NHBs) as they make quite a large contribution in exclusive B-->Xsl+l- decays at large tanf beta regions of parameter space of SUSY models, since part of SUSY contributions is proportional to tanf 3beta. The analysis of decay rate, forward-backward asymmetries, lepton polarization asymmetries, and the polarization asymmetries of the Lambda baryon in Lambdab-->Lambdal+l- show that the values of these physical observables are greatly modified by the effects of NHBs. In the SUSY SO(10) grand unified theory model, the new physics contribution comes from the operators which are induced by the NHBs' penguins and also from the operators having chirality opposite to that of the corresponding standard model (SM) operators. SUSY SO(10) effects show up only in the decay Lambdab-->Lambda+tau+tau- where the longitudinal and transverse lepton polarization asymmetries deviate significantly from the SM value while the effects in the decay rate, forward-backward asymmetries, and polarization asymmetries of final state Lambda baryon are very mild. The transverse lepton polarization asymmetry in Lambdab-->Lambda+tau+tau- is almost zero in the SM and in the MSSM model. However, it can reach to -0.1 in the SUSY SO(10) grand unified theory model and could be seen at the future colliders; hence this asymmetry observable will provide us useful information to probe new physics and discriminate between different models.
It is shown that in SO(10) models where the large solar and atmospheric neutrino angles come from the charged-lepton mass matrix being “lopsided”, there is a characteristic relation between the 13 mixing angle of the neutrinos and the size of the Dirac CP-violating phase in the lepton sector. This is illustrated in a recently proposed realistic and predictive model.
It is shown that, in a model in which up-type and down-type fermions acquire mass from different Higgs doublets, the anthropic tuning of the Higgs mass parameters can explain the fact that the observed masses of the d and u quarks are nearly the same with d slightly heavier. If Yukawa couplings are assumed not to scan (vary among domains), this would also help explain why t is much heavier than b. It is also pointed out that the existence of dark matter invalidates some earlier anthropic arguments against the viability of domains where the standard model Higgs has positive mu2, but makes other even stronger arguments possible.
In a recent paper we pointed out that the mixing of the light neutrinos with heavy gauge singlet states could reconcile the Z-pole data from e+e- colliders and the numu (nu¯mu) scattering data from the NuTeV experiment at Fermilab. We further noted that the mixing angle required to fit the data is much larger than what would be expected from the conventional seesaw mechanism. In this paper, we show how such mixings can be arranged by a judicious choice of the neutrino mass texture. We also argue that by invoking the unification of the Dirac mass matrix for the up-type quarks and the neutrinos, the mass of the heavy states can naturally be expected to lie in the few TeV range. The model is strongly constrained by the lepton flavor changing process mu-->egamma which requires lepton universality to be violated in the charged channel.
Understanding similarities and differences of properties of quark and leptons is one of the milestones on the way to underlying physics. Several observations, if not accidental, can strongly affect implications of data: (i) nearly tri-bimaximal character of lepton mixing, (ii) special neutrino symmetries, (iii) the QLC-relations. We consider possible connections between quarks and leptons which include the quark-lepton symmetry and unification, approximate universality, and quark-lepton complementarity. Presence of new neutrino states and their mixing with the left or/and right handed neutrinos can be the origin of additional differences of quarks and leptons.
A brief review is given of some ideas for explaining neutrino masses and mixings within the context of supersymmetric grand unification. Emphasis is put on so-called lopsided models.
In weak-interaction models with spontaneous parity nonconservation, based on the gauge group SU(2)/sub L/ x SU(2)/sub R/ x U(1), we obtain the following formula for the neutrino mass: m..nu../sub e/ approx. = m/sub e/ ²/gmW-italic/sub R/, where W/sub R/ is the gauge boson which mediates right-handed weak interactions. This formula, valid for each lepton generation, relates the near maximality of observed parity nonconservation at low energies to the smallness of neutrino masses.
The idea that fermions acquire their masses via a universal seesaw mechanism can provide a plausible explanation for the mass hier- archy ,u,d{}{10}^{\mathrm{-{}}4}. A minimal SU(3{}SU(2 {}SU(2{}U(1{)}_{\mathrm{B}\mathrm{-{}}\mathrm{L}} grand unifiable realization is presented. Whereas the fermionic representation is enlarged to include SU(2{}SU(2 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.
Long-wavelength vacuum oscillations between neutrinos can explain all the existing results from the chlorine, water-Cherenkov, and new gallium solar neutrino detectors. They predict distinctive energy dependences and seasonal time dependences that can be measured in solar neutrino experiments currently being constructed.
Data from the Kamiokande detector were used to study the atmospheric (nu(mu) + nu(mu)BAR)/(nu(e) + nu(e)BAR) ratio in the multi-GeV energy range. The observed ratio of mu-like to e-like events relative to the calculated ratio, (mu/e)data/(mu/e)MC = 0.57(+0.08/-0.07) +/- 0.07, suggests that the atmospheric (nu(mu) + nu(mu)BAR)/(nu(e) + nu(e)BAR) ratio is smaller than expected for these neutrino energies. Also studied was the zenith-angle dependence of the above ratio. Results of an analysis of neutrino oscillations are presented.
Results are presented of the observation of atmospheric neutrino interactions in the Kamiokande detector in an exposure of 4.92 kt yr. The observed ratio of single ring μ-events to e-events suggests that the atmospheric vμ/ve ratio is smaller than expected. The implications of these results for neutrino oscillations are discussed.
We have observed 277 fully contained events in the KAMIOKANDE detector. The number of electron-like single-prong events is in good agreement with the predictions of a Monte Carlo calculation based on atmospheric neutrino interactions in the detector. On the other hand, the number of muon-like single-prong events is 59±7% (statistical error) of the predicted number of the Monte Carlo calculation. We are unable to explain the data as the result of systematic detector effects or uncertainties in the atmospheric neutrino fluxes.
There is a persistent discrepancy between the calculated and observed flavor ratio of cosmic ray neutrinos in the atmosphere, particularly in the energy region below 1 GeV. In this talk I review the status of calculations of atmospheric neutrinos and discuss possible interpretations in terms of neutrino oscillations. Limits from neutrino-induced upward muons are also considered.
In view of large uncertainties in the prediction of the boron neutrino flux from the Sun we consider the magnitude of this flux, PhiB, as a parameter to be found from experiment. A consistent description of the data in terms of neutrino resonant conversion admits PhiB/PhiB0 = 0.4-2.5 in small mixing domain and PhiB/PhiB0 = 1-3 in large mixing domain (here PhiB0≡5.7.106 cm-2s-1 is the flux in the reference SSM). Variations of the flux within these intervals enlarge the allowed region of mixing angles to sin22theta = (0.06-2) . 10-2 and sin22theta = 0.2-0.9 correspondingly. If the value of PhiB is about the one measured by Kamiokande, the data fix the region Deltam2 ~ (4-9) . 10-6 eV2 and sin22theta ~ (0.6-2) . 10-3 (``very small mixing solution''). We comment on the possibility to measure the neutrino parameters and the original boron neutrino flux in future experiments. On leave from Institute for Nuclear Research, Russian Academy of Sciences, 117312 Moscow, Russia.
The effect of coherent forward scattering must be taken into account when considering the oscillations of neutrinos traveling through matter. In particular, for the case of massless neutrinos for which vacuum oscillations cannot occur, oscillations can occur in matter if the neutral current has an off-diagonal piece connecting different neutrino types. Applications discussed are solar neutrinos and a proposed experiment involving transmission of neutrinos through 1000 km of rock.
We examine in detail the possibility that the low rates observed in the chlorine solar neutrino experiment are due to vacuum oscillations between just two neutrino species — a possibility which remains viable over a finite mass range. We calculate the expected signals, seasonal variations, and effects of time-averaging for both chlorine and gallium based solar neutrino detectors. These provide unique signals for such oscillations, and thus also allow them to be distinguished from the recently proposed resonant neutrino conversion process, as well as from other possible causes of the observed suppression. Finally we display several striking signatures of oscillations relevant to future experiments which may be sensitive to the incident neutrino energy spectrum.
The possibility of calculating the flavor mixing angles in the six-quark theory based on the gauge group SU(2)L × SU(2)R × U(1) is discussed. The t quark mass can be computed in terms of the u, d, s, c, and b quark masses. We estimate mt ≈ 10…11 GeV. Phenomenological implications with respect to the decays of b and t flavored particles are described. The B mesons decay into charmed particles.
Solar model independent tests of the vacuum oscillation and MSW solutions of the solar neutrino problem are considered. Detailed predictions for time (seasonal) variations of the signals due to neutrino oscillations in vacuum are given for the future solar neutrino detectors (SNO, Super-Kamiokande, BOREXINO, HELLAZ). Results on the distortions of the spectra of 8B neutrinos, and of e− from the reaction ν + e− → ν + e− induced by 8B neutrinos, are presented in the cases of vacuum oscillations or MSW transitions for a large number of values of the relevant parameters. The possibilities to distinguish between the vacuum oscillation, the MSW adiabatic, and the MSW nonadiabatic transitions in the future solar neutrino experiments are discussed.
We show how two different scales for oscillations between e and μ neutrinos, characterized by different mixing angles and very different effective mass scales, can arise in a simple and theoretically attractive framework, so as to be relevant to both solar neutrino and accelerator-reactor experiments. One scale characterizes direct oscillations, which can accommodate the MSW approach to the solar neutrino problem, whereas the other can be considered as arising indirectly, through virtual transitions involving the τ neutrino with a mass ∼ 1 eV. This indirect transition allows the possibility of observable oscillations at accelerator and reactor energies. We discuss specifically the parameters suggested by a recent experiment at Los Alamos within this framework.
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 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 εu,d,e which are related by the SO(10) symmetry properties. Their values are determined by the ratio of the GUT scale Mx ⋍ 1016 GeV to a higher (possibly string) scale . 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 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 Mt < 165 GeV, while the lower bound Mt > 160 GeV implies . tanβ can vary from 1.4 to 1.7. The proton decaying d = 5 operators qqql are naturally suppressed.
A very simple extension of the Standard Model to include an Abelian family symmetry is able to describe the hierarchy of quark and lepton masses and their mixing angles together with the unification of gauge couplings. We consider the implications of this model for neutrino masses and mixing angles and show that they are determined up to a discrete ambiguity corresponding to the representation content of the Higgs sector responsible for the Majorana mass matrix.
It was recently shown by the authors that the Fritzsch Ansatz for the quark mass matrices prescribed at the supersymmetric grand unified scale is compatible with a moderately heavy top quark (m(t) congruent-to 120-150 GeV). Here we extend the Ansatz to incorporate the charged leptons and the neutrinos. It is found that the nu(e)-nu(mu) mixing angle is small and consistent with the MSW solution of the solar neutrino puzzle. Furthermore, the model predicts observable nu(mu)-nu(tau) oscillations with sin(2)2theta(mutau) congruent-to 0.1 and nu(tau) mass in the 1-3 eV range.
A generation mechanism of the quark and lepton masses in gauge models with horizontal symmetry is proposed. It is based on the mixing of quark-lepton families with heavy horizontal fermions, acquiring large masses directly after breaking of horizontal symmetry. A simple implementation of this mechanism for the SU(3)H × SU(2)L × SU(2)R × U(1) model is given. The following results are obtained for the Kobayashi-Maskawa mixing angles: s1 ≅ ( md m > s)1 2, s2 ≅ ( mc mt)1 2, s3 ≅ ( ms mb)1 2. The extension of this mechanism to GUTs is discussed.
We propose a new mechanism for CP violation in supersymmetric theories. CP is broken spontaneously at a high energy scale, and at the weak scale this CP violation appears only in soft, supersymmetry breaking operators. The weak interactions conserve CP and the strong CP problem is solved. We investigate in detail an SU(5) theory which incorporates this mechanism. Phases in squark masses are responsible for CP violation in the kaons via ε. The penguin diagram is real and can give large contributions to ΔI = 1/2 kaon decays without contributing to ε′/ε. A non-zero neutron electric dipole moment should be detected soon, while ε′/ε is likely to be as small as 10−4. The cosmological baryon asymmetry is produced by the same phase which is ultimately responsible for ε. This yields a natural expectation for nB/nγ in the vicinity of the observed value.
We present an ansatz for the quark and lepton mass matrices, derivable from SO(10) type GUTs, which accomodates a heavy (>92GeV) top quark and permits large mixings in the vμ→vτ sector (as suggested by the recent Kamiokande and IMB data on the atmospheric neutrinos). The well known asymptotic relations mb = mτ, and mdms = memμ all hold to a good approximation. Depending on vμ→vτ mixing which can be maximal, the mixing the angle rate for solar neutrino oscillations lies in the range 7.8 × 10−3≳sin2 2θegm ≳ 2.1 × 10−2. For the 71Ga experiment the event rate, normalized against the standard solar model prediction of 132 SNU, is estimated to be between 80 and 20 SNU.
The seesaw mechanism is implemented for all quarks and leptons in the standard model of strong and electroweak interactions based on the gauge group SU(3\ifmmode\times\else\texttimes\fi{}SU(2\ifmmode\times\else\texttimes\fi{}U(1). This requires the introduction of a set of new fermions that are singlets of the weak-interaction group SU(2. Two models are constructed: one with discrete symmetries and another with Peccei-Quinn symmetry. The Higgs sector of the second model is identical to the Dine-Fischler-Srednicki model.
In this paper we present a new Ansatz for fermion mass matrices in the context of supersymmetric grand unified theories. We are able to fit the 13 parameters, associated with quark and lepton masses and mixing angles, and the ratio of Higgs vacuum expectation values (VEV's) which enters any supersymmetric theory, in terms of 8 input parameters; hence, we have 6 predictions. The top quark is predicted to have a mass in the range 176 to 190 GeV, where the upper bound results from the assumption of perturbative unification, and the lower bound is sensitive to the experimental value of Vcb. Predictions are also made for ms, ms/md, ||Vub/Vcb||, the ratio of Higgs VEV's, and the CP-violating phase of the Kobayashi-Maskawa matrix.
Recent experimental data confirm the solar-neutrino problem and imply new neutrino physics. We review some of the less discussed proposals to solve this problem: (1) maximal vacuum mixing of three neutrino flavors, (2) vacuum oscillation of two neutrino flavors, and (3) neutrino decay. Each of these three solutions can fit the {sup 37}Cl and Kamiokande-II solar-neutrino flux measurements. Their implications for the continuing {sup 71}Ga experiments and for other, future experiments are discussed.
A deficit of solar neutrinos compared to the standard solar model prediction has been measured in both the Homestake and Kamiokande-II experiments, with quite different detectors. We analyze the parameter space for oscillations of two neutrinos to find regions that can explain both experiments. Long-wavelength vacuum oscillation solutions are found with {delta}{ital m}{sup 2}{congruent}0.5--2.5{times}10{sup {minus}10} eV{sup 2} and sin{sup 2}2{theta}{approx gt}0.7. Matter-enhanced oscillation solutions are found for (i) nonadiabatic transitions having {delta}{ital m}{sup 2}{theta}{sup 2}{approx}10{sup {minus}8} eV{sup 2} and {delta}{ital m}{sup 2}{approx}3{times}10{sup {minus}8}--2{times}10{sup {minus}5} eV{sup 2}, and (ii) adiabatic transitions having {delta}{ital m}{sup 2}{approx}10{sup {minus}7}--10{sup {minus}4} eV{sup 2} with sin{sup 2}2{theta}{approx gt}0.5. The two-neutrino long-wavelength and matter-enhanced solutions predict {sup 71}Ga measurements in the ranges 50--80 and 5--115 solar-neutrino units (SNU), respectively, compared to 130 SNU without oscillations. We emphasize the distinctive features of each solution, including their predictions for future {nu}-{ital e} scattering experiments and detectable seasonal variations in the long-wavelength solutions. We also find the range of three-neutrino vacuum oscillation solutions.
Neutrino interactions from a 7.7 kton yr exposure of the IMB-3 detector are analyzed. A total of 935 contained events radiating over {similar to}50 MeV of {hacek C}erenkov-equivalent energy and consistent with atmospheric neutrino interactions are identified. Of these, 610 have a single {hacek C}erenkov ring. Single-ring interactions are efficiently separated into those containing a showering particle (produced mainly by {nu}{sub {ital e}}) and those containing a nonshowering particle (produced mainly by {nu}{sub {mu}}). In the momentum range 100{lt}{ital p}{sub {ital e}}{lt}1500 MeV/{ital c} and 300{lt}{ital p}{sub {mu}}{lt}1500 MeV/{ital c}, the fraction of nonshowering events is 0.36{plus minus}0.02(stat){plus minus}0.02(syst). Based on detailed models of neutrino production and interaction, a fraction of 0.51{plus minus}0.01(stat){plus minus}0.05(syst) is expected. This deficit of nonshowering, or excess of showering, events relative to the total is supported by an independent analysis of muon decay signals. In the same sample 33{plus minus}2(stat)% of events are accompanied by one or more muon decays, while 43{plus minus}1(stat)% are expected. Further studies that could reduce systematic errors and discover the cause of these discrepancies are suggested.
We consider the most general solar model, using the neutrino fluxes as free parameters constrained only by the solar luminosity, and show that the combined solar neutrino data exclude any astrophysical solution at 98\% C.L.\ Our best fit to the Be and B fluxes is respectively 7\% and 374\% of the standard solar model prediction, but only with a large (5.6 for 1 d.f.). This best fit to the fluxes contradicts explicit nonstandard solar models, which generally reduce the B flux more than the Be. Those models are well parameterized by a single parameter, the central temperature.
We present an extension of the left-right-symmetric model by including extra singlet quarks and leptons, which leads to calculable - mixing and an ultralight Dirac mass for the neutrino. For a mass in the tera-electron-volt range, the neutrino masses can be in the right range to explain the solar neutrino puzzle via the Mikheyev-Smirnov-Wolfenstein oscillation amplification mechanism. Crucial for our results is a ``see-saw''-type mechanism for the smallness of the d-quark masses.
A model is proposed which predicts that is large, that one family (e, u, and d) has only radiatively generated\char22{}and hence small\char22{}masses, and that at the unification scale {m}_{\tau{}}^{0}{} but {m}_{\mu{}}^{0}{} and {}. An essential feature of the model is a close connection between the pattern of breaking of unified gauge symmetry at large scales and the pattern of fermion masses at low scales, which gives a group-theoretical understanding of many features of the quark and lepton masses.
The atmospheric neutrino flux is measured using a 3.4-kt yr exposure of the IMB-3 detector. Single-ring events are classified as showering or nonshowering using the geometry of the {hacek C}erenkov pattern. A simulation of neutrino interactions and three models of atmospheric neutrino production are used to predict the composition of the sample. Showering-nonshowering character is strongly correlated with the flavor of the neutrino parent. In the lepton momentum range {ital p}{lt}1500 MeV/{ital c}, we find that nonshowering events comprise (41{plus minus}3{plus minus}2syst)% of the total. The fraction expected is (51{plus minus}5(syst))%.
The fermion masses and mixings are derived from a small number of input parameters. The resulting six predictions are consistent with data and have interesting consequences for future experiments. The top quark is heavy, near 188 GeV; its precise mass is sensitive to Vcb.
We show that minimal SO(10) Grand Unification models where the fermions have Yukawa couplings to only one (complex) {\bf 10} and one {\bf 126} of Higgs scalars lead to a very predictive neutrino spectrum. This comes about since the standard model doublet contained in the {\bf 126} of Higgs (needed for the see--saw mechanism) receives an induced vacuum expectation value at tree--level, which, in addition to correcting the bad asymptotic mass relations and , also relates the Majorana neutrino mass matrix to observables in the charged fermion sectors. We find that (i) the mixing angle relevant for the solar neutrinos can be considerably smaller than the Cabibbo angle and lies in the range , (ii) mixing is sin, (iii) the mixing angle is large, , and (iv) , implying that oscillations should be accessible to forthcoming experiments. Comment: 14 pages, Latex
Two-neutrino oscillations in vacuum are studied as a possible solution of the solar neutrino problem. New constraints on the parameter sn2, characterizing the mixing of the electron neutrino with another active or sterile neutrino, as well as on the mass--squared difference, dm2, of their massive neutrino components, are derived using the latest results from the four solar neutrino experiments. Oscillations into a sterile neutrino are ruled out at 99 % C.L. by the observed mean event rates even if one includes the uncertainties of the standard solar model predictions in the analysis. Comment: 10 pages + 3 figures attached as postscript files, IFP-480-UNC and Ref. SISSA 177/93/EP (Updated Version which takes into account the latest GALLEX results from 30 runs)
We give a general prescription for deriving quark and lepton mass matrices
with ``texture'' zeros in the framework of superstring inspired SO(10)
models. The key to our approach is a new way to naturally implement the
doublet--triplet splitting which enables us to obtain symmetric quark and
lepton mass matrices which have different structures in the up and the down
quark sectors. We illustrate our method by deriving the Georgi--Jarlskog
texture which has six predictions in the flavor sector, and then show how it
generalizes to other symmetric texture models.
A new procedure is developed which enables one to start from the quark and lepton mass and mixing data at the low scale and construct mass matrices that exhibit simple SO(10) structure at the supersymmetric-grand-unification scale. This approach is applied to the present data involving quark and charged lepton masses, the quark mixing matrix and the nonadiabatic solar neutrino and atmospheric neutrino depletion effects. In terms of just 12 model parameters suggested by the procedure for the 5 mass matrices, we can reproduce remarkably well all the masses and mixing parameters for the scenario considered.
We study the see-saw enhancement mechanism in presence of the right-handed phases of the Dirac neutrino mass matrix and the Majorana mass matrix. The enhancement condition given by Smirnov is modified. We point out that the see-saw enhancement could be obtained due to the right-handed phases even if the Majorana matrix is proportional to the unit matrix. We show a realistic Dirac mass matrix which causes the see-saw enhancement. Comment: 12 pages, no figures, LaTex
It is shown that almost all features of the quark and lepton masses can be
satisfactorily and simply explained without family symmetry, including the
threefold mass hierarchy among the generations, and the relations , , , , , , and . Various aspects of the
group theory of SO(10) play an essential role in explaining these relations.
The form of the mass matrices, rather than being imposed arbitrarily, emerges
naturally from a simple structure at the unification scale. This structure
involves only vector, spinor and adjoint representations. There are distinctive
and testable predictions for and the neutrino mixing angles.
A new procedure proposed recently enables one to start from the quark and lepton mass and mixing data at the low scale and construct mass matrices which exhibit simple SO(10) structure at the SUSY GUT scale. We elaborate here on the numerical details which led us to an SO(10) model for the quark and lepton mass matrices that explain the known quark data at the low scale along with the observed depletions of solar- and atmospheric-neutrinos. We also apply the procedure to a second scenario incorporating the solar-neutrino depletion and a 7 eV tau-neutrino for the cocktail model of mixed dark matter but find the SO(10) model deduced in this case does not exhibit as simple a structure as that observed for the first scenario.
It is a well--known problem that in supersymmetric models there are new CP--violating phases which, if unsuppressed, would give a neutron electric dipole moment to times the present experimental limit. Here we propose that these new phases are suppressed by CP invariance, which is broken spontaneously at a high scale and that this breaking shows up at low energies only through a universal phase of the gaugino masses. It is shown that this can well fit both and of the neutral Kaon system. The electric dipole moments of the neutron and the electron should be not much below present limits. A model incorporating these ideas in a very economical way is presented. Comment: 14 pages in Plain LaTeX, BA-93-48, 6 figures (Feynman diagrams) not included, available on request
A new approach for deducing the theory of fermion masses at the scale of grand unification is proposed. Combining SO(10) grand unification, family symmetries and supersymmetry with a systematic operator analysis, the minimal set of fermion mass operators consistent with low energy data is determined. Exploiting the full power of SO(10) to relate up, down and charged lepton mass matrices, we obtain predictions for 7 of the mass and mixing parameters. The assumptions upon which the operator search and resulting predictions are based are stressed, together with a discussion of how the predictions are affected by a relaxation of some of the assumptions.The masses of the heaviest generation, and , are generated from a single renormalizable Yukawa interaction, while the lighter masses and the mixing angles are generated by non-renormalizable operators of the grand unified theory. The hierarchy of masses and mixing angles is thereby related to the ratio of grand to Planck scales, . An explicit realization of the origin of such an economical pattern of operators is given in terms of a set of spontaneously broken family symmetries. In the preferred models the top quark is found to be heavy: GeV, and is predicted to be very large. Predictions are also given for and the amount of CP violation. Stringent tests of these theories will be achieved by more precise measurements of and and by measurements of CP violation in neutral B meson decays. Comment: 65 pages, 22 figures or complete manuscript available by mail. LBL-33531
The see-saw mechanism of neutrino mass generation may enhance lepton mixing up to maximal even if the Dirac mass matrices of leptons have structure similar to that in the quark sector. Two sets of conditions for such an enhancement are found. The first one includes the see-saw generation of heavy Majorana masses for right-handed neutrinos and a universality of Yukawa couplings which can follow from the unification of neutrinos with new superheavy neutral leptons. The second set is related to lepton number symmetry of the Yukawa interactions in the Dirac basis of neutrinos. Models which realize these conditions have strong hierarchy or strong degeneration of Majorana masses of the right-handed neutrinos. Comment: 16 pages, plain TeX document, Institute for Advanced Study number AST 93/14
We develop a systematic analysis of quark mass matrices which, starting with the measured values of quark masses and mixing angles, allows for a model independent search for all possible (symmetric or hermitian) mass matrices having texture zeroes at the unification scale. A survey of all six and five texture zero structures yields a total of five possible solutions which may be distinguished by improved measurements of the CKM matrix elements and which may readily be extended to include lepton masses with the Georgi-Jarlskog texture. The solutions naturally suggest a parameterisation for the mass matrices based on a perturbative expansion and we present some speculations concerning the origin of such structure. Comment: 30 pages, RAL-93-010 UFIFT-93-06
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: , , . We construct 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 0.5 and the Cabibbo angle is forced to be . The top quark is naturally in the 100 GeV range, but not too heavy: 150 GeV. Inspired by the mass matrices obtained in the model for quarks, we suggest an ansatz also including charged leptons. The differences between u-, d- and e-type fermions are simply parametrized by three complex coefficients \eps{u}, \eps{d} and \eps{e}. Additional consistent predictions are obtained: =100-150 MeV and 0.75.
Using renormalization group techniques, we examine several interesting relations among masses and mixing angles of quarks and leptons in the Standard Model. We extend the analysis to the minimal supersymmetric extension to determine its effect on these mass relations. Remarkably Supersymmetry allows for these relations to be satisfied at a single grand unified scale. Comment: 25 pages, 18 postscript figures not included, (uses phyzzx)
- Phys
- H Rev
- D Arason
- E Castano
- P Pirad
- P Ramond
- R G Ramond
- G G Roberts
- K S Ross
- Q Babu
- Phys Shafi
- K S Lett
- R N Babu
- G Mohapatra
- Anderson
Phys. Rev. D45, 4192 (1991); H. Arason, D. Castano, E. Pirad and
P. Ramond, Phys. Rev. D47, 232 (1992); P. Ramond, R.G. Roberts
and G.G. Ross, Nucl. Phys. B406, 19 (1993); K.S. Babu and Q. Shafi,
Phys. Lett.B294, 235 (1992); Phys. Lett. B311, 172 (1993); K.S. Babu
and R.N. Mohapatra, Phys. Rev. Lett. 70, 2845 (1993); G. Anderson
et. al., Phys. Rev. D49, 3660 (1994); C. Albright and S. Nandi, Phys.
Rev. Lett. 73, 930 (1994); Phys. Rev. D52, 410 (1995); H. Dreiner,
G. Leontaris, S. Lola, G. Ross and C. Scheich, Nucl. Phys. B436, 461
(1995).
- Z Berezhiani
- Phys Lett
- D Chang
- R N Mohapatra
- A Davidson
- K Wali
Z. Berezhiani, Phys. Lett. 129B, 99 (1983); Phys. Lett. B355, 178
(1995); D. Chang and R.N. Mohapatra, Phys. Rev. Lett. 58, 1600
(1987); A. Davidson and K. Wali, Phys. Rev. Lett. 59, 393 (1987); S.
- A Yu
- Smirnov
A. Yu. Smirnov, Phys. Rev. D48, 3264 (1993);
- K S Babu
- J C Pati
- F Wilczek
K.S. Babu, J.C. Pati and F. Wilczek, Phys. Lett. B359, 351 (1995);
- S Dimopoulos
- L Hall
- S Raby
S. Dimopoulos, L. Hall and S. Raby, Phys. Rev. Lett. 64, 1984 (1992);
- M Tanimoto
- Phys
- Lett
M. Tanimoto, Phys.
Lett. B345, 477 (1995).
- D Casper
B335, 237 (1994); IMB Collaboration: D. Casper et. al., Phys. Rev.
- K S Babu
- S M Barr
K.S. Babu and S.M. Barr, Phys. Rev. Lett. 72, 2831 (1994).