1,787 research outputs found
Standard-like Models as Type IIB Flux Vacua
We construct new semi-realistic Type IIB flux vacua on
orientifolds with three- and four- Standard Model (SM) families and up to three
units of quantized flux. The open-string sector is comprised of magnetized
D-branes and is T-dual to supersymmetric intersecting D6-brane constructions.
The SM sector contains magnetized D9-branes with negative D3-brane charge
contribution. There are large classes of such models and we present explicit
constructions for representative ones. In addition to models with one and two
units of quantized flux, we also construct the first three- and four-family
Standard-like models with supersymmetric fluxes, i.e. comprising three units of
quantized flux. Supergravity fluxes are due to the self-dual NS-NS and R-R
three-form field strength and they fix the toroidal complex structure moduli
and the dilaton. The supersymmetry conditions for the D-brane sector fix in
some models all three toroidal K\"ahler moduli. We also provide examples where
toroidal K\" ahler moduli are fixed by strong gauge dynamics on the ``hidden
sector'' D7-brane. Most of the models possess Higgs doublet pairs with Yukawa
couplings that can generate masses for quarks and leptons. The models have
(mainly right-) chiral exotics.Comment: 31 page
Flavor changing neutral current constraints on standard-like orbifold models
We examine for standard-like orbifold compactification models the constraints
due to quarks and leptons generation non-universality of soft supersymmetry
breaking interactions. We follow the approach initiated by Ibanez and Lust and
developed by Brignole, Ibanez and Munoz. The breaking of supersymmetry is
represented in terms of dilaton and moduli auxiliary field components and,
consistently with a vanishing cosmological constant, is parametrized in terms
of the dilaton-moduli mixing angle and the gravitino mass scale
. The soft breaking interactions (gaugino masses, squarks and sleptons
mass matrices, scalars interactions A and B coupling constants) are calculable
as a function of these parameters and of the discrete set of modular weight
parameters specifying the modular transformation properties of the low-energy
fields. We solve the renormalization group one-loop equations for the full set
of gauge, Yukawa and supersymmetry breaking coupling constants.Comment: 32 page
Axions in gravity with torsion
We study a scenario allowing a solution of the strong charge parity problem
via the Peccei-Quinn mechanism, implemented in gravity with torsion. In this
framework there appears a torsion-related pseudoscalar field known as
Kalb-Ramond axion. We compare it with the so-called Barbero-Immirzi axion
recently proposed in the literature also in the context of the gravity with
torsion. We show that they are equivalent from the viewpoint of the effective
theory. The phenomenology of these torsion-descended axions is completely
determined by the Planck scale without any additional model parameters. These
axions are very light and very weakly interacting with ordinary matter. We
briefly comment on their astrophysical and cosmological implications in view of
the recent BICEP2 and Planck data.Comment: 7 pages, no figures, comments and references added, published versio
Multiple Schr\"odinger pictures and dynamics in shortcuts to adiabaticity
A Schr\"odinger equation may be transformed by unitary operators into
dynamical equations in different interaction pictures which share with it a
common physical frame, i.e., the same underlying interactions, processes and
dynamics. In contrast to this standard scenario, other relations are also
possible, such as a common interaction-picture dynamical equation corresponding
to several Schr\"odinger equations that represent different physics. This may
enable us to design alternative and feasible experimental routes for operations
that are a priori difficult or impossible to perform. The power of this concept
is exemplified by engineering Hamiltonians that improve the performance or make
realizable several shortcuts to adiabaticity
Neutrino Oscillations from Supersymmetry without R-parity - Its Implications on the Flavor Structure of the Theory
We discuss here some flavor structure aspects of the complete theory of
supersymmetry without R-parity addressed from the perspective of fitting
neutrino oscillation data based on the recent Super-Kamiokande result. The
single-VEV parametrization of supersymmetry without R-parity is first reviewed,
illustrating some important features not generally appreciated. For the flavor
structure discussions, a naive, flavor model independent, analysis is
presented, from which a few interesting things can be learned.Comment: 1+10 pages latex, no figure; Invited talk at NANP 99 conference,
Dubna (Jun 28 - Jul 3) --- submission for the proceeding
A Classification of 3-Family Grand Unification in String Theory I. The SO(10) and E_6 Models
We give a classification of 3-family SO(10) and E_6 grand unification in
string theory within the framework of conformal field theory and asymmetric
orbifolds. We argue that the construction of such models in the heterotic
string theory requires certain Z_6 asymmetric orbifolds that include a Z_3
outer-automorphism, the latter yielding a level-3 current algebra for the grand
unification gauge group SO(10) or E_6. We then classify all such Z_6 asymmetric
orbifolds that result in models with a non-abelian hidden sector. All models
classified in this paper have only one adjoint (but no other higher
representation) Higgs field in the grand unified gauge group. In addition, all
of them are completely anomaly free. There are two types of such 3-family
models. The first type consists of the unique SO(10) model with SU(2) X SU(2) X
SU(2) as its hidden sector (which is not asymptotically-free at the string
scale). This SO(10) model has 4 left-handed and 1 right-handed 16s. The second
type is described by a moduli space containing 17 models (distinguished by
their massless spectra). All these models have an SU(2) hidden sector, and 5
left-handed and 2 right-handed families in the grand unified gauge group. One
of these models is the unique E_6 model with an asymptotically-free SU(2)
hidden sector. The others are SO(10) models, 8 of them with an asymptotically
free hidden sector at the string scale.Comment: 35 pages, Revtex 3.0, one eps figure (to appear in Phys. Rev. D
Aspects of Type I String Phenomenology
We study different phenomenological aspects of compact, D=4, N=1 Type IIB
orientifolds considered as models for unification of the standard model and
gravity. We discuss the structure of the compactification, string and
unification scales depending on the different possible D-brane configurations.
It is emphasized that in the context of Type I models the
hierarchy problem is substantially alleviated and may be generated by
geometrical factors. We obtain the effective low-energy supergravity Lagrangian
and derive the form of soft SUSY-breaking terms under the assumption of
dilaton/moduli dominance. We also discuss the role of anomalous U(1)'s and of
twisted moduli in this class of theories. A novel mechanism based on the role
of singularities is suggested to achieve consistency with gauge coupling
unification in low string scale models.Comment: 47 pages, Latex2e, 4 EPS figures, using epsfig. Minor typos and
references adde
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