728 research outputs found
Exploring the SO(32) Heterotic String
We give a complete classification of Z_N orbifold compactification of the
heterotic SO(32) string theory and show its potential for realistic model
building. The appearance of spinor representations of SO(2n) groups is analyzed
in detail. We conclude that the heterotic SO(32) string constitutes an
interesting part of the string landscape both in view of model constructions
and the question of heterotic-type I duality.Comment: 21 pages, 5 figure
Actinic keratosis-related signs predictive of squamous cell carcinoma in renal transplant recipients: a nested case-control study
Background Squamous cell carcinoma (SCC) and intraepidermal carcinoma (IEC) commonly arise in actinically damaged skin
Localized tadpoles of anomalous heterotic U(1)'s
We investigate the properties of localized anomalous U(1)'s in heterotic
string theory on the orbifold T^6/Z_3. We argue that the local four dimensional
and original ten dimensional Green-Schwarz mechanisms can be implemented
simultaneously, making the theory manifestly gauge invariant everywhere, in the
bulk and at the fixed points. We compute the shape of the Fayet-Iliopoulos
tadpoles, and cross check this derivation for the four dimensional auxiliary
fields by a direct calculation of the tadpoles of the internal gauge fields.
Finally we study some resulting consequences for spontaneous symmetry breaking,
and derive the profile of the internal gauge field background over the
orbifold.Comment: 35 pages, LaTeX, with figure
Constraining the primordial spectrum of metric perturbations from gravitino and moduli production
We consider the production of gravitinos and moduli fields from quantum
vacuum fluctuations induced by the presence of scalar metric perturbations at
the end of inflation. We obtain the corresponding occupation numbers, up to
first order in perturbation theory, in terms of the power spectrum of the
metric perturbations. We compute the limits imposed by nucleosynthesis on the
spectral index for different models with constant . The results show
that, in certain cases, such limits can be as strong as , which is
more stringent than those coming from primordial black hole production.Comment: 16 pages, LaTeX, 5 figures. Corrected figures, new references
included. Final version to appear in Phys. Rev.
Supersymmetry Breakdown at a Hidden Wall
We consider hidden sector supersymmetry breakdown in the strongly coupled
heterotic theory of Ho\v{r}ava and Witten. Using effective
field theory methods in four dimensions, we can show that gravitational
interactions induce soft breaking terms in the observable sector that are of
order of the gravitiono mass. We apply these methods to the mechanism of
gaugino condensation at the hidden wall. Although the situation is very similar
to the weakly coupled case, there is a decisive difference concerning the
observable sector gaugino mass; with desirable phenomenological as well as
cosmological consequences.Comment: 29 pages, latex, no figures, To appear in Nuclear Physics B. Minor
change
Models of Dynamical Supersymmetry Breaking with Gauged Symmetry
We present simple models of dynamical supersymmetry breaking with gauged
U(1)_R symmetry. The minimal supersymmetric standard model and supersymmetric
SU(5) GUT are considered as the visible sector. The anomaly cancellation
conditions for U(1)_R are investigated in detail and simple solutions of the
R-charge assignments are found. We show that this scenario of dynamical
supersymmetry breaking is phenomenologically viable with the gravitino mass of
order 1 TeV or 10 TeV.Comment: 15 pages, uses REVTEX macro, No figure
Resolutions of C^n/Z_n Orbifolds, their U(1) Bundles, and Applications to String Model Building
We describe blowups of C^n/Z_n orbifolds as complex line bundles over
CP^{n-1}. We construct some gauge bundles on these resolutions. Apart from the
standard embedding, we describe U(1) bundles and an SU(n-1) bundle. Both
blowups and their gauge bundles are given explicitly. We investigate ten
dimensional SO(32) super Yang-Mills theory coupled to supergravity on these
backgrounds. The integrated Bianchi identity implies that there are only a
finite number of U(1) bundle models. We describe how the orbifold gauge shift
vector can be read off from the gauge background. In this way we can assert
that in the blow down limit these models correspond to heterotic C^2/Z_2 and
C^3/Z_3 orbifold models. (Only the Z_3 model with unbroken gauge group SO(32)
cannot be reconstructed in blowup without torsion.) This is confirmed by
computing the charged chiral spectra on the resolutions. The construction of
these blowup models implies that the mismatch between type-I and heterotic
models on T^6/Z_3 does not signal a complication of S-duality, but rather a
problem of type-I model building itself: The standard type-I orbifold model
building only allows for a single model on this orbifold, while the blowup
models give five different models in blow down.Comment: 1+27 pages LaTeX, 2 figures, some typos correcte
Fermion Masses and Gauge Mediated Supersymmetry Breaking from a Single U(1)
We present a supersymmetric model of flavor. A single U(1) gauge group is
responsible for both generating the flavor spectrum and communicating
supersymmetry breaking to the visible sector. The problem of Flavor Changing
Neutral Currents is overcome, in part using an `Effective Supersymmetry'
spectrum among the squarks, with the first two generations very heavy. All
masses are generated dynamically and the theory is completely renormalizable.
The model contains a simple Froggatt-Nielsen sector and communicates
supersymmetry breaking via gauge mediation without requiring a separate
messenger sector. By forcing the theory to be consistent with SU(5) Grand
Unification, the model predicts a large tan beta and a massless up quark. While
respecting the experimental bounds on CP violation in the K-system, the model
leads to a large enhancement of CP violation in B-(B bar) mixing as well as in
B decay amplitudes.Comment: LaTeX, 25 pages, 8 figure
Non-standard embedding and five-branes in heterotic M-Theory
We construct vacua of M-theory on S^1/Z_2 associated with Calabi-Yau
three-folds. These vacua are appropriate for compactification to N=1
supersymmetry theories in both four and five dimensions. We allow for general
E_8 x E_8 gauge bundles and for the presence of five-branes. The five-branes
span the four-dimensional uncompactified space and are wrapped on holomorphic
curves in the Calabi-Yau space. Properties of these vacua, as well as of the
resulting low-energy theories, are discussed. We find that the low-energy gauge
group is enlarged by gauge fields that originate on the five-brane
world-volumes. In addition, the five-branes increase the types of new E_8 x E_8
breaking patterns allowed by the non-standard embedding. Characteristic
features of the low-energy theory, such as the threshold corrections to the
gauge kinetic functions, are significantly modified due to the presence of the
five-branes, as compared to the case of standard or non-standard embeddings
without five-branes.Comment: 34 pages, Latex 2e with amsmath, typos removed, factors corrected,
refs improve
String-Unification, Universal One-Loop Corrections and Strongly Coupled Heterotic String Theory
We derive the universal threshold corrections in heterotic string theory
including a continuous Wilson line. Unification of gauge and gravitational
couplings is shown to be possible even within perturbative string theory. The
relative importance of gauge group dependent and independent thresholds on
unification is clarified. Equipped with these results we can then attempt an
extrapolation to the strongly coupled heterotic string -- M-theory. We argue
that such an extrapolation might be meaningful because of the holomorphic
structure of the gauge coupling function and the close connection of the
threshold corrections to the anomaly cancelation mechanism.Comment: 28 LaTex pages with 2 fig
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