Search

The gauge coupling constant unification at the low ($O$(TeV)) scale can be obtained just in four dimensions, without help of the power like renormalization group evolution in extra dimensions, due to the presence of some extra particle states at intermediate scales. We show explicit examples of such extra states in the range of 100 GeV -- 1 TeV which can be easily observed on future colliders and can have important impact on the particle phenomenology. The problems of the low scale grand unification and proton stability are also discussed., Comment: 12 pages, Latex, 2 figures

A new possibility for solving the strong CP-problem is suggested,which assumes that apart of the ordinary world of observable particles described by standard model, there exits a mirror sector of particles and two sectors share the same Peccei-Quinn symmetry realized {\it a l\`a} Weinberg-Wilczek model. The mirror gauge group is completely analogous to that of the standard model for ordinary particles but having somewhat larger electroweak scale,which in turn implies the infrared scale $\Lambda'$ of the mirror strong interactions has to be larger than the ordinary QCD scale $\Lambda$. In this way, the axion mass and interaction constants are actually determined by mirror sector scales $v'$ and $\Lambda'$, while the $\theta$ terms are simultaneously cancelled in both sectors due to mirror symmetry. The experimental and astrophysical limits on such an axion is discussed. An interesting parameter window is found where $f_a \sim {\rm few}\times 10^4$ GeV whereas the axion mass is $\sim 1$ MeV., Comment: 13 LaTex pages, 3 Postscript figures

There can exist a parallel `mirror' world which has the same particle physics as the observable world and couples the latter only gravitationally. The nucleosynthesis bounds demand that the mirror sector should have a smaller temperature than the ordinary one. By this reason its evolution should be substantially deviated from the standard cosmology as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are concerned. Starting from an inflationary scenario which could explain the different initial temperatures of the two sectors, we study the time history of the early mirror universe. In particular, we show that in the context of the GUT or electroweak baryogenesis scenarios, the baryon asymmetry in the mirror world should be larger than in the observable one and in fact the mirror baryons could provide the dominant dark matter component of the universe. In addition, analyzing the nucleosynthesis epoch, we show that the mirror helium abundance should be much larger than that of ordinary helium. The implications of the mirror baryons representing a kind of self-interacting dark matter for the large scale structure formation, the CMB anysotropy, the galactic halo structures, microlensing, etc. are briefly discussed., Comment: 16 pages, Latex, including 5 eps. Figures. Small textual modifications. To appear in Phys. Lett. B

We propose new textures for the fermion Yukawa matrices which are generalizations of the so-called Stech ansatz. We discuss how these textures can be realized in supersymmetric grand unified models with horizontal symmetry SU(3)_H among the fermion generations. In this framework the mass and mixing hierarchy of fermions (including neutrinos) can emerge in a natural way. We emphasize the central role played by the SU(3)_H adjoint Higgs field which reduces SU(3)_H to U(2)_H at the GUT scale. A complete SO(10)\times SU(3)_H model is presented in which the desired Yukawa textures can be obtained by symmetry reasons. The phenomenological implications of these textures are thoroughly investigated. Among various realistic possibilities for the Clebsch factors between the quark and lepton entries, we find three different solutions which provide excellent fits of the quark masses and CKM mixing angles. Interestingly, all these solutions predict the correct amount of CP violation via the CKM mechanism, and, in addition, lead to an appealing pattern of the neutrino masses and mixing angles. In particular, they all predict nearly maximal 23 mixing and small 12 mixing in the lepton sector, respectively in the range needed for the explanation of the atmospheric and solar neutrino anomaly., Comment: 52 LaTeX pages, 3 postscript figures, uses epsfig and feynmp. Typos corrected; in section 3 the presentation of the SO(10) x SU(3)_H model is expanded to motivate the pattern of both Higgs VEVs and Yukawa matrices. To be published on Nucl. Phys. B

The Pseudo-Goldstone Boson (PGB) emission could provide a very efficient mechanism for explaining the cosmic Gamma Ray Bursts (GRBs). The PGBs could be produced during the merging of two compact objects like two neutron stars or neutron star - black hole, and then decay into electron-positron pairs and photons at distances ~ 100-1000 km. In this way, a huge energy (up to more than 10^{54} erg) can be deposited into the outer space with low baryon density in the form of ultrarelativistic e^+e^- plasma, the so called fireball, which originates the observed gamma-ray bursts. The needed ranges for the PGB parameters are: mass of order MeV, coupling to nucleons g_{aN} ~ few x 10^{-6} and to electrons g_{ae} ~ few x 10^{-9}. Interestingly enough, the range for coupling constants correspond to that of the invisible axion with the Peccei-Quinn symmetry breaking scale V ~ few x 10^5 GeV, but the mass of the PGB is many orders of magnitude larger than what such a scale would demand to an axion. Neither present experimental data nor astrophysical and cosmological arguments can exclude such an ultramassive axion, however the relevant parameters' window is within the reach of future experiments. Another exciting point is that our mechanism could explain the association of some GRBs with supernovae type Ib/c, as far as their progenitor stars have a radius ~ 10^4 km. And finally, it also could help the supernova type II explosion: PGBs emitted from the core of the collapsing star and decaying in the outer shells would deposit a kinetic energy of the order of 10^{51} erg. In this way, emission of such an axion-like particle could provide an unique theoretical base for understanding the gamma ray bursts and supernova explosions., Comment: 15 pages, 3 figures

It is shown that a Nambu-Goldstone (NG) field may be coherently produced by a large number of particles in spite of the fact that the NG bosons do not couple to flavor conserving scalar densities like $\bar{\psi}\psi$. If a flavor oscillation process takes place the phases of the pseudo-scalar or flavor violating densities of different particles do not necessarily cancel each other. The NG boson gets a macroscopic source whenever the total (spontaneously broken) quantum number carried by the source particles suffers a net increase or decrease in time. If the lepton numbers are spontaneously broken such classical NG (majoron) fields may significantly change the neutrino oscillation processes in stars pushing the observational capabilities of neutrino-majoron couplings down to $m_{\nu}/300$ GeV., Comment: 11 pages, updated, to appear in PRD

The comparison of the CKM mixing angles with the leptonic mixings implied by the recent atmospheric and solar neutrino data exhibits an interesting complementarity. This pattern can be understood in the context of the SU(5) grand unification, assuming that the fermion mass matrices have Fritzsch-like structures but are not necessarily symmetric. (The present contribution is based on the paper in ref. \cite{az}.), Comment: Latex file + espcrc2.sty, 5 pages, 3 postscript figures included. Talk given at the Int. Workshop ``Particles in Astrophysics and Cosmology: from Theory to Observation'', May 3-8, 1999, Valencia, Spain. To appear in Nucl. Phys. Proc. Suppl

The atmospheric neutrino data imply large mixing between the $\nu_\mu$ and $\nu_\tau$ states, $\theta_{23} = (45\pm 12)^\circ$, while the MSW solution to the solar neutrino problem needs very small mixing angle $\theta_{12} = (2\pm 1)^\circ$. In the quark sector the situation is rather opposite -- the 23 mixing is tiny, $\theta_{23}\simeq 2^\circ$, versus reasonable 12 mixing, $\theta_{12}\simeq 13^\circ$. We show that such complementary patterns of the quark and leptonic mixings could naturally emerge in the context of the SU(5) grand unification, assuming that the fermion mass matrices have the Fritzsch-like structures but their off-diagonal entries are not necessarily symmetric. Such a picture exhibits a `see-saw' like correspondence between the quark and leptonic mixing patterns so that the smaller the quark mixing angle is, the larger the corresponding leptonic mixing angle becomes. This fact simply follows from the fermion multiplet structure in SU(5). We also discuss a model with horizontal symmetry U(2) in which the discussed pattern of the mass matrices can arise rather naturally., Comment: Latex file, 23 pages, 9 postscript figures. Typos fixed; new figures and references added; some discussions extended and refined

We study the effects of possible flavor-violating operators in theories with the TeV scale quantum gravity, in which the ordinary matter is localized on a 3-brane embedded in the space with $N$ extra dimensions, whereas gravity propagates in the bulk. These operators are scaled by the fundamental Planck mass $M_{Pf}\sim$ TeV and must be suppressed by the gauge family symmetries. We study suppression of the most dangerous and model-independent operators. Several points emerge. First, we show that the Abelian symmetries can not do the job and one has to invoke non-Abelian $U(2)_F$ (or $U(3)_F$) symmetries. However, even in this case there emerge severe restrictions on the fermion mixing pattern and the whole structure of the theory. In order not to be immediately excluded by the well-known bounds, the horizontal gauge fields {\it must} be the bulk modes, like gravitons. For the generic hierarchical breaking pattern the four-fermion operators induced by the tree-level exchange of the bulk gauge fields are unsuppressed for $N = 2$. For $N > 3$ the suppression factor goes as a square of the largest $U(2)_F$-non-invariant Yukawa coupling, which implies the lower bound $M_{Pf} > 10$ TeV or so from the $K^0 - \bar K^0$ system. Situation is different in the scenarios when flavor Higgs fields live on a ($3 + N'$)-brane of lower dimensionality than the gauge fields. The further suppression of gauge-mediated operators can be achieved by an explicit construction: for instance, if $U(2)_F$ is broken by a vacuum expectation value of the doublet, the troublesome operators are suppressed in the leading order, due to custodial SO(4) symmetry of the Higgs-gauge quartic coupling., Comment: 18 pages, Latex

We discuss an initial condition on the superpotential couplings of an SU(5) theory which allows the R-violating term L d^c Q but avoids the simultaneous presence of L L e^c + d^c d^c u^c. This same condition keeps under control the products of pairs of different couplings lambda_{ijk} L_i d^c_j Q_k, which are more strongly constrained by flavour-changing-neutral-current limits. In our view, this observation makes relatively more plausible the interpretation of the high-Q^2 Hera anomaly, if real, as caused by squark production., Comment: 4 pages, no figures. References and footnote added, misprints corrected

The anomalous gauge $U(1)_A$ symmetry which could emerge in the context of the string theories can be very useful ingredient towards builting the complete supersymmetric SO(10) model. We present an example of the $SO(10)\times U(1)_A$ model which provides the ``all order'' solution to the doublet-triplet splitting problem via the missing VEV mechanism -- the Planck scale corrections only can induce the mu-term naturally of order 1 TeV. An interesting feature of this model is that all relevant GUT scale VEVs are defined by the single dimensional parameter in the Higgs superpotential, so that the SO(10) symmetry breaks down to the MSSM practically at one step, without intermediate stages. The colour Higgsino mediated d=5 operators can be naturally suppressed. We also extend the model by implementing $U(1)_A$ as a horizontal symmetry for explaining the fermion mass and mixing pattern, and obtain a predictive texture for fermion masses. This model implies a moderate value of $\tan\beta$ ($\sim 6-10$) and leads to five predictions for the low energy observables. It also leads to the neutrino masses and mixing pattern that could naturally explain both the atmospheric and solar neutrino problems. In addition, a remarkable interplay of the SO(10) and $U(1)_A$ symmetries guarantees an automatic R parity conservation at any order in $M_P^{-1}$, and also suppresses the Planck scale induced B and L violating d=5 operators to the needed level., Comment: 18 pages, LATEX, no figures

We present the supersymmetric $SU(5)$ models which provide a simple ``all order'' solution to the doublet-triplet splitting problem through the missing doublet mechanism. The crucial role is played by the anomalous $U(1)_A$ gauge symmetry and no additional discrete or global symmetries are needed. Remarkably, such models can be realized even if the 75-plet Higgs is replaced by the standard 24-plet. The same $U(1)_A$ symmetry can also guarantee an exact or approximate conservation of R parity, by suppressing the B and L violating operators to the needed level. The neutrino masses and the proton decay via $d=5$ operators are also examined. We also extend the model by incorporating $U(1)_A$ as a horizontal symmetry for explaining the fermion mass and mixing hierarchy. Interestingly, in this scheme the necessary mild violation of the troublesome $SU(5)$ degeneracy between the down quark and the charged lepton masses can be induced by certain R-parity violating operators., Comment: 16 pages, LATEX, no figures

The horizontal symmetry $U(3)_H$ can greatly help in solving the flavor problems in the supersymmetric grand unification. We consider the $SU(5)\times U(3)_H$ model and show that it leads to the remarkable relations between the fermion mass matrices and the soft SUSY breaking terms. Dangerous supersymmetric contributions to the flavor-changing phenomena are naturally suppressed. The possible extensions to the $SO(10)\times U(3)_H$ model are also outlined., Comment: Latex, 5 pages - some more discussions added

The concept of non-abelian horizontal symmetry $SU(3)_H$ can greatly help in understanding the fermion and sfermion flavour structures in supersymmetric grand unification. For the sake of demonstration the $SU(5)\times SU(3)_H$ model, suggested earlier in ref. \cite{PLB85}, is revisited. We show that under very simple and natural assumption it links the sfermion mass pattern to those of fermions in a remarkable way. All dangerous supersymmetric flavour-changing contributions are naturally suppressed in a general case, independently of the concrete texture for fermion mass matrices. Nevertheless, within this framework we present an example of predictive model for fermion masses and mixing, which leads to 7 consistent predictions for the low energy observables. [Based on talks given at Int. Workshop {\em `SUSY 96'}, Univ. of Maryland, 29 May - 1 June 1996 (to appear on Proceedings), and II US-Polish Workshop {\em `Physics from Planck Scale to Electroweak Scale'}, Warsaw, 28-30 March 1996.], Comment: 12 pages, LATEX, no figures

In an analogy to the case of axion, which converts the $\Theta$-angle into a dynamical degree of freedom, we are trying to imagine a situation where the quark mixing angles turn out to be dynamical degrees of freedom (pseudo-Goldstone bosons), and their vacuum expectation values are obtained from the minimization of the vacuum energy. We present an explicit supersymmetric model with horizontal symmetry, where such a mechanism can be realized. It implies one relation between the quark masses and the CKM mixing angles: $s_{13}s_{23}/s_{12}=(m_s/m_b)^2$, which is fulfilled within present experimental accuracy. We believe, however, that the idea might be more general than this concrete model, and it can be implemented in more profound frameworks., Comment: Latex, 25 pages - as it will appear in Nucl. Phys. B

The problem of fermion masses and mixings is discussed in the context of supersymmetric grand unification theories. Some predictive frameworks based on the $SU(5)$, $SO(10)$ and $SU(6)$ models are reviewed. [Based on lectures delivered at the ICTP Summer School on `High Energy Physics and Cosmology', Trieste, Italy, 3-28 July 1995 (to appear on Proceedings), and XIX Int. Conference on {\em Particle Physics and Astrophysics in the Standard Model and Beyond}, Bystra, Poland, 19-26 September 1995], Comment: 36 pages, Latex

The neutrino long wavelength (just-so) oscillation is reconsidered as a solution to the solar neutrino problem. In the light of the presently updated results of the four solar neutrino experiments, the data fit in the just-so scenario substantially improves and becomes almost as good as in the MSW scenario. Surprising result of our analysis is that best fit is achieved when the oscillation occurs only between two neutrino states: switching on the oscillation into third neutrino increases the $\chi^2$ value. Namely, we consider the vacuum oscillation scenario in the three-neutrino system (4 parameters) and find out that the $\chi^2$ minimum is always achieved in the {\it two} parameter subspace in which actually only {\it two} neutrino states oscillate. This holds in the framework of any solar model with relaxed prediction of the various neutrino fluxes. The possible theoretical implications of this observation are also discussed., Comment: 9 pages, Latex, 4 figures (not included, available upon request from ROSSI@ferrara.infn.it)

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 $\bar{m}_{e,u,d}$ 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 $\tan\beta\sim 1$. The inter-family hierarchy is first generated in a sector of hypothetical superheavy fermions and then transfered inversely to ordinary quarks and leptons by means of the universal seesaw mechanism. The Yukawa matrices are simply parametrized by the small complex coefficients $\eps_{u,d,e}$ which are related by the $SO(10)$ symmetry properties. Their values are determined by the ratio of the GUT scale $M_X\simeq 10^{16}$ GeV to a higher (possibly string) scale $M\simeq 10^{17}-10^{18}$ 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, we compute the $u,d,s$ quark masses, top mass and $\tan\beta$. The top quark is naturally in the 100 GeV range, but with upper limit $M_t<165$ GeV, while the lower bound $M_t>160$ GeV implies $m_s/m_d>22$. $\tan\beta$ can vary from 1.4 to 1.7. The proton decaying $d=5$ operators $qqql$ are naturally suppressed., Comment: 11 pages, Latex, 2 figures not included

The supersymmetric $SU(6)$ model equipped by the flavour-blind discrete gauge symmetry $Z_3$ is considered. It provides simultaneous solution to the doublet-triplet splitting problem, $\mu$-problem and leads to natural understanding of fermion flavour. The Higgs doublets arise as Goldstone modes of the spontaneously broken {\em accidental} global symmetry $SU(6)\times U(6)$ of the Higgs superpotential. Their couplings to fermions have peculiarities leading to the consistent picture of the quark and lepton masses and mixing, without invoking the horizontal symmetry or zero texture concepts. In particular, the only particle that has direct $O(1)$ Yukawa coupling with the Higgs doublet is top quark. Other fermion masses arise from the higher order operators, with natural mass hierarchy described in terms of small ratios $\eps_\Sigma=V_\Sigma/V_H$ and $\eps_H=V_H/M$, where $V_H$ and $V_\Sigma$ correspondingly are the $SU(6)$ and $ SU(5)$ symmetry breaking scales, and $M$ is a large (Planck or string) scale. The model automatically implies $b-\tau$ Yukawa unification. Specific mass formulas are also obtained, relating the down quark and charged lepton masses. Neutrinos get small ($\sim 10^{-5}\,$eV) masses which can be relevant for solving the solar neutrino problem via long wavelength vacuum oscillation., Comment: 15 pages, LATEX, 4 figures are included

We study an extension of the supersymmetric standard model with four families and gauged horizontal symmetry $SU(4)_H$, in which R parity automatically follows as a consequence of gauge invariance and of the field content of the model. Beyond ensuring R parity conservation, the horizontal symmetry allows for the dynamical generation of a hierarchical pattern of fermion masses, without the need of any ad hoc choice of small Yukawa couplings. The structure of the mass matrices implies that the fourth family does not mix with the other three, and that the $b',t',\tau',\nu'$ masses are all naturally in the 100 GeV range. The model has other interesting phenomenological implications. The scale of the horizontal symmetry breaking is constrained by cosmological and astrophysical arguments to be $\sim 10^{11}$ GeV. Then the late $b'$ decays could explain a magnitude of the isotropic cosmic gamma flux. In addition, a lower bound of a few eV is found for the mass of the $\tau$-neutrino, which can thus provide a hot component for the cosmological dark matter. Due to R parity conservation, the lightest supersymmetric particle is stable and can provide the cold component. The $\nu_e$ and $\nu_\mu$ masses can naturally be in the correct ranges for a solution of the solar or atmospheric neutrino problems via neutrino oscillations., Comment: 12 pages, LATEX

The doublet-triplet splitting problem is perhaps the most problematic aspect of supersymmetric grand unified theories. It can be argued that the most natural reason for the Higgs doublets to be light is that they are pseudo-Goldstone bosons associated with the spontaneous breakdown of an accidental global symmetry. In this paper we discuss the possibility of implementing this idea in the SU(6) model of refs. \cite{Zur,Bar2,Bar3,Bar4}. We show that although it is simple to generate an accidental symmetry of the renormalizable terms of the potential, it is quite difficult to construct a model which allows for the preservation of the accidental symmetry in the nonrenormalizable terms. We summarize the constraints on such models and then give three different ways to construct a superpotential where the dangerous mixing terms are sufficiently suppressed even in the presence of nonrenormalizable operators. With these examples we demonstrate the existence of consistent models implementing the Higgs as pseudo-Goldstone boson scheme. We extend one of the three examples to include fermion masses. We also show that when restricted to regular group embeddings the only possible models without light triplets are trivial generalizations of the SU(6) model we consider., Comment: 39 pages, plain LaTeX

The supersymmetric $SU(6)$ model accompanied by the flavour-blind discrete symmetry $Z_3$ can succesfully deal with such key problems of SUSY GUTs, as are the gauge hierarchy/doublet-triplet splitting, $\mu$-problem and flavour problem. The Higgs doublets arise as Goldstone modes of the spontaneously broken {\em accidental} global $SU(6)\times U(6)$ symmetry of the Higgs superpotential. Their couplings to fermions have peculiarities leading to the consistent picture of the quark and lepton masses and mixing, without invoking any of horizontal symmetry/zero texture concepts. In particular, the only particle that has direct Yukawa coupling with the Higgs doublet is top quark. Other fermion masses appear from the higher order operators, with natural mass hierarchy. Specific mass formulas are also obtained. [On the basis of talks given at the Int. Workshop "Physics from Planck Scale to Electroweak Scale", Warsaw, Poland, 21-24 September 1994, and at the III Trieste Conference "Recent Developments in the Phenomenology of Particle Physics", Trieste, Italy, 3-7 October 1994.], Comment: 18 pages, LATEX, 3 figures included. Some minor latex and textual errors are corrected, and few refs. are added

In most supersymmetric models the stability of the proton is ensured by invoking R-parity. A necessary ingredient to enforce R-parity is the possibility of distinguishing the lepton superfields from the Higgs ones. This is generally achieved either by assuming different charges under some matter parity, or by assigning the superfields to different representations of a unified gauge group. We want to put forward the idea that the replica of the fermion generations, which constitute an intrinsic difference between the fermions and the Higgs superfields, can give a clue to understand R-parity as an accidental symmetry. More ambitiously, we suggest a possible relation between proton stability and the actual number of fermion generations. We carry out our investigation in the framework of non-Abelian horizontal gauge symmetries. We identify $SU(4)_H$ as the only acceptable horizontal gauge group whichcan naturally ensure the absence of R parity violating operators, without conflicting with other theoretical and phenomenological constraints. We analyze a version of the supersymmetric standard model equipped with a gauged horizontal $SU(4)_H$, in which R-parity is accidental. The model predicts four families of fermions, it allows for the dynamical generation of a realistic hierarchy of fermion masseswithout any ad hoc choice of small Yukawa couplings, it ensures in a natural way the heaviness of all the fourth family fermions (including the neutrino) and it predicts a {\it lower} limit for the $\tau$-neutrino mass of a few eV. The scale of the breaking of the horizontal symmetry can be constrained rather precisely in a narrow window around $\sim 10^{11}$ GeV. Some interesting astrophysical and cosmological implications of the model are addressed as well., Comment: Revised version : improved analysis of the horizontal gauge groups. One numerical error corrected. 21 pages, LaTex, no figures

We present a new predictive approach based on SUSY $SO(10)$ theory. The inter-family hierarchy is first generated in the sector of hypothetical superheavy fermions and then transfered inversely to ordinary quarks and leptons by means of the universal seesaw mechanism. The obtained mass matrices are simply parametrized by two small complex coefficients $\eps_u$ and $\eps_d$, which can be given by the ratio of the GUT scale $M_G\simeq 10^{16}$ GeV and some higher scale $M\simeq 10^{17}-10^{18}$ GeV (presumably superstring scale). The model provides a possibility for doublet-triplet splitting without fine tuning and the Higgsino mediated $d=5$ operators for the proton decay are naturally suppressed. Our ansatz provides the correct {\em qualitative} picture of fermion mass hierarchy and mixing pattern, provided that $\eps_d/\eps_u\sim 10$. The running masses of the first family fermions: electron, u-quark and d-quark obey an approximate $SO(10)$ symmetry limit. At GUT scale we have: $u\sim d\simeq 3e$, $(\frac{\eps_u}{\eps_d})c\sim s\simeq \frac{1}{3}\mu$ and $(\frac{\eps_u}{\eps_d})^2t\sim b\simeq \tau$. The Cabibbo angle is large: $s_{12}\simeq \sqrt{m_d/m_s}$ while other mixing angles have their natural size: $s_{23}\sim m_s/m_b$ and $s_{13}\sim m_d/m_b$. We have many strong {\em quantitative} predictions though no special `zero' texture is utilized (in contrast to the known predictive frameworks). Namely, taking as input the lepton, c-quark and b-quark masses, $m_s/m_d$ mass ratio and Cabibbo angle, we can obtain the light (u,d,s) quark masses, top mass and $\tan\beta$. The top quark is naturally in the 100 GeV range, but not too heavy: $m_t<165$ GeV. The lower bound $M_t>150$ GeV (160 GeV), Comment: 22 pages, 5 figures (cut out as separate postscript file), LATEX, INFN-FE-05-94

It is well known that the matter can significantly alter the picture of neutrino oscillation \cite{W} or neutrino decay \cite{BV}. Here we show that the presence of dense matter induces also the decay of {\it massless} majoron, a Goldstone boson associated with the spontaneous lepton number violation, into a couple of neutrinos with the same (or in some cases also opposite) helicities. We calculate the rates of such matter induced majoron decays in various cases, depending on the neutrino type and the chemical content of the medium, and analyse their properties., Comment: 11 pages, no figures, LATEX, INFN-FE-04-94

After a brief review of the flavour problem we present a new predictive framework based on SUSY $SO(10)$ theory, where the first family plays a role of the mass unification point. The inter-family hierarchy is first generated in a sector of superheavy fermions and then transfered in an inverse way to ordinary quarks and leptons by means of the universal seesaw mechanism. The obtained mass matrices are simply parametrized by two small coefficients which can be given by the ratio of the GUT and superstring compactification scales. The model allows a natural (without fine tuning) doublet-triplet splitting. It has a strong predictive power, though no special texture is utilized in contrast to the known predictive frameworks. Namely, the model implies that $m_b=4-5$ GeV, $m_s=100-150$ MeV, $m_u/m_d=0.5-0.7$ and $\tan\beta<1.1$. The Top quark is naturally in the 100 GeV range, but not too heavy: $m_t<150$ GeV. All CKM mixing angles are in correct range. The Higgsino mediated $d=5$ operators for the proton decay are naturally suppressed. {On the basis of talks given at the XVI International Warsaw Meeting on Elementary Particle Physics "New Physics with New Experiments", Kazimierz, Poland, 24-28 May 1993, and at the II Gran Sasso Summer Institute "From Particle Physics to Cosmology", Gran Sasso National Laboratory, Italy, 6-17 September 1993.}, Comment: 22 pages (standard LATEX) + 1 Figure (postscript file, cut out and print separately), Ferrara preprint INFN-FE-13-93

Effects of the dense matter can induce the neutrino decay even if neutrinos are stable in vacuum. This is due to coherent interactions with matter which lead to energy level-splitting between the neutrino and antineutrino states and thereby provide available phase space for the majoron emission. We show that the matter induced decay can be a plausible candidate for the explanation of solar neutrino deficit, provided that there exist new flavour-changing weak range interactions of neutrino with matter constituents, and constant of $\tau$-neutrino coupling to the majoron is sufficiently large. This mechanism naturally implies the hierarchy between the ratios Z=(measured signal)/(SSM expectation) for Ga-Ge, nu_e-e scattering and Cl-Ar experiments - Z_{GA}>Z_{K}>Z_{Cl}. The important feature of the matter induced decay is the prediction of solar antineutrino flux with substantially degraded energy spectrum compared to solar neutrinos. This scenario can be unambiguously tested by future solar neutrino detectors BOREXINO/BOREX and SNO., Comment: 15 pages, No Figures, LATEX file, INFN FE-08-93

The up-down splitting within quark families increases with the family number: m_u ~ m_d, m_c > m_s, m_t >> m_b. We show an approach that realizes this feature of the spectrum in a natural way. We suggest that the mass hierarchy is first generated by radiative effects in a sector of heavy isosinglet fermions, and then projected to the ordinary light fermions by means of a seesaw mixing. The hierarchy appears then inverted in the light fermion sector. We present a simple left-right symmetric gauge model in which the P- and CP-parities and an isotopical "up-down" symmetry are softly (or spontaneously) broken in the Higgs potential. Experimentally consistent predictions are obtained. The Cabibbo angle is automatically in the needed range: Theta_C ~ 0.2. The top quark is naturally heavy, but not too heavy: m_t < 150 GeV., Comment: 8 pages, LATEX, LMU-08/92

Zee-type models with Majorons naturally incorporate the 17 keV neutrino but in their minimal version fail to simultaneously solve the solar neutrino puzzle. If there is a sterile neutrino state, we find a particularly simple solution to the solar neutrino problem, which besides $\nu_{17}$ predicts a light Zeldovich-Konopinski-Mahmoud neutrino $\nu_{light}=\nu_e+\nu_{\mu}^c$ with a magnetic moment being easily as large as $10^{-11}\mu_B$ through the Barr-Freire-Zee mechanism., Comment: 11 pages, 2 figures (not included but available upon request), LaTex, IC/92/216, SISSA-141/92/EP, LMU-10/92

We discuss gravitationally induced masses and mass splittings of Majorana, Zeldovich-Konopinski-Mahmoud and Dirac neutrinos. Among other implications, these effects can provide a solution of the solar neutrino puzzle. In particular, we show how this may work in the 17 keV neutrino picture., Comment: 10 pages, IC/92/79, SISSA-83/92/EP, LMU-04/92 (the preprint number has been corrected; no other changes)