541 research outputs found

    Flavor Unification and Discrete Nonabelian Symmetries

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    Grand unified theories with fermions transforming as irreducible representations of a discrete nonabelian flavor symmetry can lead to realistic fermion masses, without requiring very small fundamental parameters. We construct a specific example of a supersymmetric GUT based on the flavor symmetry Δ(75)\Delta(75) --- a subgroup of SU(3)SU(3) --- which can explain the observed quark and lepton masses and mixing angles. The model predicts tanβ25\tan\beta \simeq 2-5 and gives a τ\tau neutrino mass mνMp/GFMGUT2=10m_\nu\simeq M_p/G_F M_{GUT}^2 = 10 eV, with other neutrino masses much lighter. Combined constraints of light quark masses and perturbative unification place flavor symmetry breaking near the GUT scale; it may be possible to probe these extremely high energies by continuing the search for flavor changing neutral currents.Comment: 24 pages, UCSD-PTH-93-30 (uuencoded file; requires epsf.tex, available from this bulletin board

    Hidden flavor symmetries of SO(10) GUT

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    The Yukawa interactions of the SO(10) GUT with fermions in 16-plets (as well as with singlets) have certain intrinsic ("built-in") symmetries which do not depend on the model parameters. Thus, the symmetric Yukawa interactions of the 10 and 126 dimensional Higgses have intrinsic discrete Z2×Z2Z_2\times Z_2 symmetries, while the antisymmetric Yukawa interactions of the 120 dimensional Higgs have a continuous SU(2) symmetry. The couplings of SO(10) singlet fermions with fermionic 16-plets have U(1)3U(1)^3 symmetry. We consider a possibility that some elements of these intrinsic symmetries are the residual symmetries, which originate from the (spontaneous) breaking of a larger symmetry group GfG_f. Such an embedding leads to the determination of certain elements of the relative mixing matrix UU between the matrices of Yukawa couplings Y10Y_{10}, Y126Y_{126}, Y120Y_{120}, and consequently, to restrictions of masses and mixings of quarks and leptons. We explore the consequences of such embedding using the symmetry group conditions. We show how unitarity emerges from group properties and obtain the conditions it imposes on the parameters of embedding. We find that in some cases the predicted values of elements of UU are compatible with the existing data fits. In the supersymmetric version of SO(10) such results are renormalization group invariant.Comment: 28 pages, a reference added, typos corrected, to be published in NP

    Dihedral Families of Quarks, Leptons and Higgs Bosons

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    We consider finite groups of small order for family symmetry. It is found that the binary dihedral group Q_6, along with the assumption that the Higgs sector is of type II, predicts mass matrix of a nearest neighbor interaction type for quarks and leptons. We present a supersymmetric model based on Q_6 with spontaneously induced CP phases. The quark sector contains 8 real parameters with one independent phase to describe the quark masses and their mixing. Predictions in the |V_{ub}|-bar{eta}, |V_{ub}|-sin 2 beta(phi_1) and |V_{ub}|-|V_{td}/V_{ts}| planes are given. The lepton sector contains also 9 parameters. A normal as well as an inverted spectrum of neutrino masses is possible, and we compute V_{e3}. We find that |V_{e3}|^2 > 10^{-4} in the case of a normal spectrum, and |V_{e3}|^2 >8 10^{-4} in the case of an inverted spectrum. It is also found that Q_6 symmetry forbids all Baryon number violating terms of d=4, and the contributions to EDMs from the A terms vanish in this model.Comment: 27 pages, 8 figure

    A microscopic theory of gauge mediation

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    We construct models of indirect gauge mediation where the dynamics responsible for breaking supersymmetry simultaneously generates a weakly coupled subsector of messengers. This provides a microscopic realization of messenger gauge mediation where the messenger and hidden sector fields are unified into a single sector. The UV theory is SQCD with massless and massive quarks plus singlets, and at low energies it flows to a weakly coupled quiver gauge theory. One node provides the primary source of supersymmetry breaking, which is then transmitted to the node giving rise to the messenger fields. These models break R-symmetry spontaneously, produce realistic gaugino and sfermion masses, and give a heavy gravitino.Comment: 24 pages, 2 figures, accepted to JHEP for publicatio

    An Attractor for Natural Supersymmetry

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    We propose an attractor mechanism which generates the "more minimal" supersymmetric standard model from a broad class of supersymmetry breaking boundary conditions. The hierarchies in the fermion masses and mixings are produced by the same dynamics and a natural weak scale results from gaugino mediation. These features arise from augmenting the standard model with a new SU(3) gauge group under which only the third generation quarks are charged. The theory flows to a strongly interacting fixed point which induces a negative anomalous dimension for the third generation quarks and a positive anomalous dimension for the Higgs. As a result, a split-family natural spectrum and the flavor hierarchies are dynamically generated.Comment: 22 pages, 4 figures; v2 refs added; v3 journal versio

    Higher Flavor Symmetries in the Standard Model

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    We initiate the study of the generalized global flavor symmetries of the Standard Model. The presence of nonzero triangle diagrams between the U(3)5U(3)^5 flavor currents and the U(1)YU(1)_Y hypercharge current intertwines them in the form of a higher-group which mixes the zero-form flavor symmetries with the one-form magnetic hypercharge symmetry. This higher symmetry structure greatly restricts the possible flavor symmetries that may remain unbroken in any ultraviolet completion that includes magnetic monopoles. In the context of unification, this implies tight constraints on the combinations of fermion species which may be joined into multiplets. Three of four elementary possibilities are reflected in the classic unification models of Georgi-Glashow, SO(10)SO(10), and Pati-Salam. The final pattern is realized non-trivially in trinification, which exhibits the sense in which Standard Model Yukawa couplings which violate these flavor symmetries may be thought of as spurions of the higher-group. Such modifications of the ultraviolet flavor symmetries are possible only if new vector-like matter is introduced with masses suppressed from the unification scale by the Yukawa couplings.Comment: 12 pages, 2 figures, 10 table

    The Standard Model on a D-brane

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    We present a consistent string theory model which reproduces the Standard Model, consisting of a D3-brane at a simple orbifold singularity. We study some simple features of the phenomenology of the model. We find that the scale of stringy physics must be in the multi-TeV range. There are natural hierarchies in the fermion spectrum and there are several possible experimental signatures of the model.Comment: 8 pages Latex, 1 fig. v2: discussion improved, added new reference

    Spacetime Reduction of Large N Flavor Models: A Fundamental Theory of Emergent Local Geometry?

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    We introduce a novel spacetime reduction procedure for the fields of a supergravity-Yang-Mills theory in generic curved spacetime background, and with large N flavor group, to linearized forms on an infinitesimal patch of local tangent space at a point in the spacetime manifold. Our new prescription for spacetime reduction preserves all of the local symmetries of the continuum field theory Lagrangian in the resulting zero-dimensional matrix Lagrangian, thereby obviating difficulties encountered in previous matrix proposals for emergent spacetime in recovering the full nonlinear symmetries of Einstein gravity. We conjecture that the zero-dimensional matrix model obtained by this prescription for spacetime reduction of the circle-compactified type I-I'-mIIA-IIB-heterotic supergravity-Yang-Mills theory with sixteen supercharges and large N flavor group, and inclusive of the full spectrum of Dpbrane charges, offers a potentially complete framework for nonperturbative string/M theory. We explain the relationship of our conjecture for a fundamental theory of emergent local spacetime geometry to recent investigations of the hidden symmetry algebra of M theory, stressing insights that are to be gained from the algebraic perspective. We conclude with a list of open questions and directions for future work.Comment: 30pgs. v6: Ref [4] added, some terminology corrected in Intro, sections 5,6. Footnote 2 clarifies the relation to hep-th/0201129v1. Acknowledgments adde

    Family Symmetries and Proton Decay

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    The proton decay modes pK0e+p\to K^0 e^+ and pK0μ+p\to K^0 \mu^+ may be visible in certain supersymmetric theories, and if seen would provide evidence for new flavor physics at extremely short distances. These decay modes can arise from the dimension five operator (Q1Q1Q2L1,2)(Q_1Q_1Q_2L_{1,2}), where QiQ_i and LiL_i are ith{i^{th}} generation quark and lepton superfields respectively. Such an operator is not generated at observable levels due to gauge or Higgs boson exchange in a minimal GUT. However in theories that explain the fermion mass hierarchy, it may be generated at the Planck scale with a strength such that the decays pK0+p\to K^0 \ell^+ are both compatible with the proton lifetime and visible at Super-Kamiokande. Observable proton decay can even occur in theories without unification.Comment: NSF-ITP-94-69, LBL-35807, DOE/ER/40561-148-INT94-00-61, 13 pages, written with harvma
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