541 research outputs found
Flavor Unification and Discrete Nonabelian Symmetries
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 --- a subgroup of --- which can explain the
observed quark and lepton masses and mixing angles. The model predicts
and gives a neutrino mass 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
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
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 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 . Such an embedding leads to the determination of certain
elements of the relative mixing matrix between the matrices of Yukawa
couplings , , , 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
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
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
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
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
We initiate the study of the generalized global flavor symmetries of the
Standard Model. The presence of nonzero triangle diagrams between the
flavor currents and the 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, , 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
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?
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
The proton decay modes and 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 , where and are
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 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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