230,764 research outputs found

### CKM and Tri-bimaximal MNS Matrices in a SU(5) x (d)T Model

We propose a model based on SU(5) x {}^{(d)}T which successfully gives rise
to near tri-bimaximal leptonic mixing as well as realistic CKM matrix elements
for the quarks. The Georgi-Jarlskog relations for three generations are also
obtained. Due to the {}^{(d)}T transformation property of the matter fields,
the b-quark mass can be generated only when the {}^{(d)}T symmetry is broken,
giving a dynamical origin for the hierarchy between m_{b} and m_{t}. There are
only nine operators allowed in the Yukawa sector up to at least mass dimension
seven due to an additional Z_{12} x Z'_{12} symmetry, which also forbids, up to
some high orders, operators that lead to proton decay. The resulting model has
a total of nine parameters in the charged fermion and neutrino sectors, and
hence is very predictive. In addition to the prediction for \theta_{13} \simeq
\theta_{c}/3 \sqrt{2}, the model gives rise to a sum rule,
\tan^{2}\theta_{\odot} \simeq \tan^{2} \theta_{\odot, \mathrm{TBM}} - {1/2}
\theta_{c} \cos\beta, which is a consequence of the Georgi-Jarlskog relations
in the quark sector. This deviation could account for the difference between
the experimental best fit value for the solar mixing angle and the value
predicted by the tri-bimaximal mixing matrix.Comment: 11 pages; v2: additional references added; minor modifications made;
conclusion unchanged; v3: version to appear in Phys. Lett.

### Neutrino Mass Matrix from S_4 Symmetry

The cubic symmetry S_4 contains A_4 and S_3, both of which have been used to
study neutrino mass matrices. Using S_4 as the family symmetry of a complete
supersymmetric theory of leptons, it is shown how the requirement of breaking
S_4 at the seesaw scale without breaking supersymmetry enforces a special form
of the neutrino mass matrix which exhibits maximal nu_mu - nu_tau mixing as
well as zero U_e3. In addition, (nu_e + nu_mu + nu_tau)/sqrt{3} is naturally
close to being a mass eignestate, thus predicting tan^2 theta_12 to be near but
not equal to 1/2.Comment: 11 pages, no figur

### Boundary Conditions and the Generalized Metric Formulation of the Double Sigma Model

Double sigma model with the strong constraints is equivalent to the normal
sigma model by imposing the self-duality relation. The gauge symmetries are the
diffeomorphism and one-form gauge transformation with the strong constraints.
We modify the Dirichlet and Neumann boundary conditions with the fully $O(D,
D)$ description from the doubled gauge fields. We perform the one-loop $\beta$
function for the constant background fields to find low energy effective theory
without using the strong constraints. The low energy theory can also be
$O(D,D)$ invariant as the double sigma model. We use the other one way to
construct different boundary conditions from the projectors. Finally, we
combine the antisymmetric background field with the field strength to redefine
a different $O(D, D)$ generalized metric. We use this generalized metric to
construct a consistent double sigma model with the classical and quantum
equivalence. We show the one-loop $\beta$ function for the constant background
fields and obtain the normal sigma model after integrating out the dual
coordinates.Comment: 32 pages, minor changes, references adde

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