Supersymmetric SO(10) for fermion masses and mixings: rank-1 structures of flavour

We consider a supersymmetric SO(10) model with a SU(3) symmetry of flavour in which fermion masses emerge via the see-saw mixing with superheavy fermions in 16+16bar representations. In this model the dangerous D=5 operators of proton decay are naturally suppressed and flavour-changing supersymmetric effects are under control. The mass matrices for all fermion types (up and down quarks, charged leptons as well as neutrinos) appear in the form of combinations of three rank-1 matrices, common to all types of fermions, with different coefficients that are successive powers of small parameters, related to each other by SO(10) symmetry properties. Two versions of the model are considered, in which approximate grand unification of masses takes place between quarks and leptons of the first family (with very small \tan\beta) or for the ones of the second family (predicting moderate \tan\beta ~ 7-8). The second version exhibits an interesting mechanism of unification of the determinants of the Yukawa matrices of all types of fermions at the GUT scale and it provides a perfect fit of the known data for fermion masses, mixing and CP-violation. It predicts a hierarchical pattern of neutrino masses with non-zero theta_e3, within 2-7 degrees. In addition, it predicts the correct sign of the baryon asymmetry of the Universe via the leptogenesys scenario.Comment: 30 Pages, 3 figures. Clarified comments on neutrino scales and on universal seesaw, updated references. Version appeared on JHE

Towards a grand unified picture for neutrino and quark mixings

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. Supp

Strong CP problem and mirror world: the Weinberg Wilczek axion revisited

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 figure

Fast Neutron - Mirror Neutron Oscillation and Ultra High Energy Cosmic Rays

If there exists the mirror world, a parallel hidden sector of particles with exactly the same microphysics as that of the observable particles, then the primordial nucleosynthesis constraints require that the temperature of the cosmic background of mirror relic photons should be smaller than that of the ordinary relic photons, T'/T < 0.5 or so. On the other hand, the present experimental and astrophysical limits allow a rather fast neutron - mirror neutron oscillation in vacuum, with an oscillation time $\tau \sim 1$ s, much smaller than the neutron lifetime. We show that this could provide a very efficient mechanism for transporting ultra high energy protons at large cosmological distances. The mechanism operates as follows: a super-GZK energy proton scatters a relic photon producing a neutron that oscillates into a mirror neutron which then decays into a mirror proton. The latter undergoes a symmetric process, scattering a mirror relic photon and producing back an ordinary nucleon, but only after traveling a distance $(T/T')^{3}$ times larger than ordinary protons. This may relax or completely remove the GZK-cutoff in the cosmic ray spectrum and also explain the correlation between the observed ultra high energy protons and far distant sources as are the BL Lacs.Comment: 14 pages; to appear in PLB (submitted 28 November 2005

Baryogenesis in Cosmological Model with Superstring-Inspired E_6 Unification

We have developed a concept of parallel existence of the ordinary (O) and hidden (H) worlds with a superstring-inspired E_6 unification, broken at the early stage of the Universe into SO(10) X U(1) - in the O-world, and SU(6)' X SU(2)' - in the H-world. As a result, we have obtained in the hidden world the low energy symmetry group G'_SM X SU(2)'_\theta, instead of the Standard Model group G_SM. The additional non-Abelian SU(2)'_\theta group with massless gauge fields, "thetons", is responsible for the dark energy. We present a baryogenesis mechanism with the B-L asymmetry produced by the conversion of ordinary leptons into particles of the hidden sector.Comment: 15 pages, 2 figure

Soft SUSY breaking contributions to proton decay

We show that in supersymmetric grand unified theories new effective D=4 and D=5 operators for proton decay are induced by soft SUSY-breaking terms, when heavy GUT gauge bosons are integrated out, in addition to the standard D=6 ones. As a result, the proton lifetime in gauge mediated channels can be enhanced or even suppressed depending on the size of the heavy Higgses soft terms.Comment: 16 pages, 2 figures, LaTeX, JHEP3 class, axodra

Inverse Hierarchy Approach to Fermion Masses

The first fermion family might play a special role in understanding the physics of flavour. This possibility is suggested by the observation that the up-down splitting within quark families increases with the family number: $m_u\sim m_d$, $m_c>m_s$, $m_t\gg m_b$. 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 $m_u/m_d>$ 0.5 and the Cabibbo angle is forced to be $\sim\sqrt{m_d/m_s}$. The top quark is naturally in the 100 GeV range, but not too heavy: $m_t<$ 150 GeV. Inspired by the mass matrices obtained in the model for quarks, we suggest an ansatz also including charged leptons. The 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: $m_s$=100-150 MeV and $m_u/m_d<$ 0.75.Comment: 19 pages (standard TeX) + 1 table (cut out and LaTeX separately) + 1 figure (cut out and postscript separately); 2 additional figures available by fax upon request, LBL-32889, LMU-13/9

A New Approach to Flavor Symmetry and an Extended Naturalness Principle

A class of non-supersymmetric extensions of the Standard Model is proposed in which there is a multiplicity of light scalar doublets in a multiplet of a non-abelian family group with the Standard Model Higgs doublet. Anthropic tuning makes the latter light, and consequently the other scalar doublets remain light because of the family symmetry. The family symmetry greatly constrains the pattern of FCNC and proton decay operators coming from scalar-exchange. Such models show that useful constraints on model-building can come from an extended naturalness principle when the electroweak scale is anthropically tuned.Comment: 31 pages, 3 figure

Anomalous U(1) symmetry and missing doublet SU(5) model

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 figure