3,288 research outputs found

### Large Lepton Mixing in a Coset-space Family Unification on $E_7/SU(5) \times U(1)^3$

We study a coset-space unification model for families based on $E_7/SU(5)
\times U(1)^3$. We find that qualitative structure of quark and lepton mass
matrices in this model describes very well the observation. We stress, in
particular, that the large mixing angle, $\sin^22\theta_{\nu_\mu\nu_\tau}
\simeq 1$, required for the atmospheric neutrino oscillation reported by the
SuperKamiokande collaboration, is naturally obtained, which is a consequence of
unparallel family structure in the present coset-space unification.Comment: 8 pages, Latex2

### A Solution to the Polonyi Problem in the Minimum SUSY-GUT

We show that the Polonyi problem is solved in the minimum SUSY-GUT model in
which a self-coupling strength for a heavy Higgs $\Sigma$, $\lambda\Sigma^{3}$,
is very small $\lambda\sim 10^{-6}$. It is stressed that with this small
$\lambda$ the mass of the physical $\Sigma$ becomes m_{\Sigma} \sim
10^{12}\GEV and the unification scale is raised up to the gravitational one,
M\simeq 2\times 10^{18}\GEV. A potential problem, however, is also pointed
out in this GUT model

### 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

### 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

### 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

### Quark Lepton Mass Hierarchies and the Baryon Asymmetry

The mass hierarchies of quarks and charged leptons as well as a large
\n_\m-\n_\t mixing angle are naturally explained by the Frogatt-Nielsen
mechanism with a nonparallel family structure of chiral charges. We extend this
mechanism to right-handed neutrinos. Their out-of-equilibrium decay generates a
cosmological baryon asymmetry whose size is quantized in powers of the
hierarchy parameter \e^2. For the simplest hierarchy pattern the neutrino
mass \bar{m}_\n= (m_{\n_\m}m_{\n_\t})^{1/2} \sim 10^{-2} eV, which is
inferred from present indications for neutrino oscillations, implies a baryon
asymmetry $n_B/s \sim 10^{-10}$. The corresponding baryogenesis temperature is
$T_B \sim 10^{10}$ GeV.Comment: 7 page

### 511 keV Gamma Ray from Moduli Decay in the Galactic Bulge

We show that the $e^++e^-$ decay of a light scalar boson of mass 1-10 MeV may
account for the fluxes of 511 keV gamma ray observed by SPI/INTEGRAL. We argue
that candidates of such a light scalar boson is one of the string moduli or a
scalar partner of the axion in a supersymmetric theory.Comment: 6 pages, no figure, we have added an appendix to describe the
dilution of the moduli by the thermal inflation and some minor correction

- …