4,244 research outputs found
Statistics of Flux Vacua for Particle Physics
Supersymmetric flux compactification of F-theory in the geometric phase
yields numerous vacua, and provides an ensemble of low-energy effective
theories with different symmetry, matter multiplicity and Lagrangian
parameters. Theoretical tools have already been developed so that we can study
how the statistics of flux vacua depend on the choice of symmetry and some of
Lagrangian parameters. In this article, we estimate the fraction of i) vacua
that have a U(1) symmetry for spontaneous R-parity violation, and ii) those
that realise ideas which achieve hierarchical eigenvalues of the Yukawa
matrices. We also learn a lesson that the number of flux vacua is reduced very
much when the unbroken symmetry is obtained from a non-trivial
Mordell--Weil group, while it is not when is in SU(5) unification. It
also turns out that vacua with an approximate U(1) symmetry forms a locus of
accumulation points of the flux vacua distribution.Comment: 51 page
Supersymmetric Grand Unification Model with the Orbifold Symmetry Breaking in the Six Dimensional Supergravity
We construct supersymmetric (SUSY) grand unification (GUT) models in the six
dimensional space-time where the GUT symmetry is broken down to the
standard-model gauge group by a simple orbifolding T^2/Z_4 or T^2/Z_6 and a
pair of massless Higgs doublets in the SUSY standard model are naturally
obtained. Since the background geometry here is simple compared with models
using the Scherk-Schwarz mechanism, one might hope for an approximate gauge
coupling unification in the present models. Here, the presence of the massless
Higgs multiplets in the bulk is quite natural, since the anomaly cancellation
in the six dimensional space-time requires N=2 hyper multiplets in the bulk,
some of which are origins of the Higgs doublets. However, the origin of the
quarks and leptons is still not clear at all.Comment: 9 pages, including 2 figures, UT-96
Higher Dimensional Supersymmetry as an Origin of the Three Families for Quarks and Leptons
In a (0,1) supersymmetric (SUSY) six-dimensional gauge theory, a gauge
fermion gives rise to box anomalies. These anomalies are completely canceled by
assuming a vector multiplet of (1,1) SUSY. With a T^2/Z_3 orbifold
compactification of the extra two dimensional space, the theory provides three
chiral multiplets and three equivalent fixed points. We regard them as the
origin of the three families of quarks and leptons. Quasi anarchy structure in
the SU(5)-5^* representation sector and hence the bimaximal mixing in the
neutrino oscillation are explained quite naturally in this framework. We also
discuss a family symmetry as a remnant of the higher-dimensional R symmetry.Comment: 12 pages, Contribution to "Peccei Fest" January 11-13,2002, a number
of comments and an appendix are adde
Geometric Origin of Large Lepton Mixing in a Higher Dimensional Spacetime
The large mixing in the lepton sector observed in the recent
neutrino-oscillation experiments strongly suggest that nature of left-handed
lepton doublets is very different from that of left-handed quark doublets. This
means that there is a big disparity between the matter multiplets 5^*'s and
10's in the SU(5) unified theory. We show that this big difference can be
explained in a six-dimensional spacetime compactified on the T^2/Z_3 orbifold.
That is, we propose to put three families of 5^*'s on three equivalent fixed
points of the orbifold and the three 10's in the two-dimensional bulk. We
construct an explicit model realizing this situation and show that the
democratic mass structure in the lepton sector is naturally obtained and hence
the model explains the observed bi-large lepton mixing and simultaneously the
required small mixing U_e3. The mass matrices and mixing in the quark sector
are also briefly discussed.Comment: 12 pages, including 1 figure and 1 table, one paragraph and two
references adde
A Solution to the Doublet-Triplet Splitting Problem in the Type IIB Supergravity
The doublet--triplet mass splitting problem is one of the most serious
problems in supersymmetric grand unified theories (GUTs). A class of models
based on a product gauge group, such as the SU(5)_{GUT} times U(3)_H or the
SU(5)_{GUT} times U(2)_H, realize naturally the desired mass splitting that is
protected by an unbroken R symmetry. It has been pointed out that various
features in the models suggest that these product-group unification models are
embedded in a supersymmetric brane world. We show an explicit construction of
those models in the supersymmetric brane world based on the Type IIB
supergravity in ten dimensions. We consider T^6/(Z_{12} times Z_2) orientifold
for the compactified six extra dimensions. We find that all of the particles
needed for the GUT-symmetry-breaking sector are obtained from the D-brane
fluctuations. The three families of quarks and leptons are introduced at an
orbifold singularity, although their origin remains unexplained. This paper
includes extensive discussion on anomaly cancellation in a given orbifold
geometry. Relation to the Type IIB string theory, realization of R symmetry as
a rotation of extra-dimensional space, and effective superpotential at low
energies are also discussed.Comment: 61 page
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