307 research outputs found
Statistics in the Landscape of Intersecting Brane Models
An approach towards a statistical survey of four dimensional supersymmetric
vacua in the string theory landscape is described and illustrated with three
examples of ensembles of intersecting D-brane models. The question whether it
is conceivable to make predictions based on statistical distributions is
discussed. Especially interesting in this context are possible correlations
between low energy observables. As an example we look at correlations between
properties of the gauge sector of intersecting D-brane models and Gepner model
constructions.Comment: Submitted for the SUSY07 proceedings, 4 pages, 2 figure
Diversity in the Tail of the Intersecting Brane Landscape
Techniques are developed for exploring the complete space of intersecting
brane models on an orientifold. The classification of all solutions for the
widely-studied T^6/Z_2 x Z_2 orientifold is made possible by computing all
combinations of branes with negative tadpole contributions. This provides the
necessary information to systematically and efficiently identify all models in
this class with specific characteristics. In particular, all ways in which a
desired group G can be realized by a system of intersecting branes can be
enumerated in polynomial time. We identify all distinct brane realizations of
the gauge groups SU(3) x SU(2) and SU(3) x SU(2) x U(1) which can be embedded
in any model which is compatible with the tadpole and SUSY constraints. We
compute the distribution of the number of generations of "quarks" and find that
3 is neither suppressed nor particularly enhanced compared to other odd
generation numbers. The overall distribution of models is found to have a long
tail. Despite disproportionate suppression of models in the tail by K-theory
constraints, the tail in the distribution contains much of the diversity of
low-energy physics structure.Comment: 48 pages, 8 figure
Power of Black Hole Physics: Seeing through the Vacuum Landscape
In this paper we generalize the black hole bound of arXiv:0706.2050 to de
Sitter spaces, and apply it to various vacua in the landscape, with a special
emphasis on slow-roll inflationary vacua. Non-trivial constraints on the
lifetime and the Hubble expansion rate emerge. For example, the general
tendency is, that for the fixed number and the increasing mass of the species,
vacua must become more curved and more unstable, either classically or quantum
mechanically. We also discuss the constraints on the lifetime of vacua in the
landscape, due to decay into the neighboring states.Comment: 33 page
Statistics of intersecting D-brane models on T^6/Z_6
We perform a statistical analysis of supersymmetric intersecting D-brane
models on the type II orientifold T^6/Z_6. After providing an analytic proof of
the finiteness of the number of possible solutions in this setup we study the
frequency distributions of properties of the gauge group and the chiral matter
content. In particular we search for models with a standard model gauge group
and discuss their statistical suppression. The results are compared with the
recent studies on T^6/Z_2xZ_2. The analysis is conducted using a statistical
method, based on the choice of random subsets of the full ensemble of
solutions. This method allows to calculate the total number of models with high
precision to 3x10^28.Comment: 29 pages, 9 figures; v2: typos corrected; v3: comments added, section
6 expande
Selection Of A Novel Aptamer Against Vitronectin Using Capillary Electrophoresis And Next Generation Sequencing
Breast cancer (BC) results in â40,000 deaths each year in the United States and even among survivors treatment of the disease may have devastating consequences, including increased risk for heart disease and cognitive impairment resulting from the toxic effects of chemotherapy. Aptamer-mediated drug delivery can contribute to improved treatment outcomes through the selective delivery of chemotherapy to BC cells, provided suitable cancer-specific antigens can be identified. We report here the use of capillary electrophoresis in conjunction with next generation sequencing to develop the first vitronectin (VN) binding aptamer (VBA-01; Kd 405 nmol/l, the first aptamer to vitronectin (VN; Kd = 405 nmol/l), a protein that plays an important role in wound healing and that is present at elevated levels in BC tissue and in the blood of BC patients relative to the corresponding nonmalignant tissues. We used VBA-01 to develop DVBA-01, a dimeric aptamer complex, and conjugated doxorubicin (Dox) to DVBA-01 (7:1 ratio) using pH-sensitive, covalent linkages. Dox conjugation enhanced the thermal stability of the complex (60.2 versus 46.5°C) and did not decrease affinity for the VN target. The resulting DVBA-01-Dox complex displayed increased cytotoxicity to MDA-MB-231 BC cells that were cultured on plasticware coated with VN (1.8âĂâ10â»â¶mol/l) relative to uncoated plates (2.4âĂâ10â»â¶ mol/l), or plates coated with the related protein fibronectin (2.1âĂâ10â»â¶ mol/l). The VBA-01 aptamer was evaluated for binding to human BC tissue using immunohistochemistry and displayed tissue specific binding and apparent association with BC cells. In contrast, a monoclonal antibody that preferentially binds to multimeric VN primarily stained extracellular matrix and vessel walls of BC tissue. Our results indicate a strong potential for using VN-targeting aptamers to improve drug delivery to treat BC
Free Fermion Orientifolds
We investigate a class of orientifold models based on tensor products of 18
Ising models. Using the same search criteria as for the comparable case of
Gepner model orientifolds we find that there are no three-family standard model
configurations with tadpole cancellation. Even if we do not impose the latter
requirement, we only find one such configuration in the special case of complex
free fermions. In order to allow a comparison with other approaches we
enumerate the Hodge numbers of the type-IIB theories we obtain. We provide
indications that there are fermionic IIB vacua that are not
orbifolds.Comment: 18 pages + Appendix; references adde
Free Fermionic Heterotic Model Building and Root Systems
We consider an alternative derivation of the GSO Projection in the free
fermionic construction of the weakly coupled heterotic string in terms of root
systems, as well as the interpretation of the GSO Projection in this picture.
We then present an algorithm to systematically and efficiently generate input
sets (i.e. basis vectors) in order to study Landscape statistics with minimal
computational cost. For example, the improvement at order 6 is approximately
10^{-13} over a traditional brute force approach, and improvement increases
with order. We then consider an example of statistics on a relatively simple
class of models.Comment: Standard Latex, 12 page
Yukawa couplings and masses of non-chiral states for the Standard Model on D6-branes on T6/Z6'
The perturbative leading order open string three-point couplings for the
Standard Model with hidden USp(6) on fractional D6-branes on T6/Z6' from
arXiv:0806.3039 [hep-th], arXiv:0910.0843 [hep-th] are computed. Physical
Yukawa couplings consisting of holomorphic Wilsonian superpotential terms times
a non-holomorphic prefactor involving the corresponding classical open string
Kaehler metrics are given, and mass terms for all non-chiral matter states are
derived. The lepton Yukawa interactions are at leading order flavour diagonal,
while the quark sector displays a more intricate pattern of mixings. While N=2
supersymmetric sectors acquire masses via only two D6-brane displacements -
which also provide the hierarchies between up- and down-type Yukawas within one
quark or lepton generation -, the remaining vector-like states receive masses
via perturbative three-point couplings to some Standard Model singlet fields
with vevs along flat directions. Couplings to the hidden sector and messengers
for supersymmetry breaking are briefly discussed.Comment: 52 pages (including 8p. appendix); 5 figures; 14 tables; v2:
discussion in section 4.1.3 extended, footnote 5 added, typos corrected,
accepted by JHE
Model building with intersecting D6-branes on smooth Calabi-Yau manifolds
We study intersecting D6-branes in Calabi-Yau manifolds that are smooth
hypersurfaces in weighted projective spaces. We develop the techniques for
calculating intersection numbers between special Lagrangian sub-manifolds
defined as fixed loci of anti-holomorphic involutions. We present global
Pati-Salam and MSSM-like models that are supersymmetric up to a decoupled
hidden sector.Comment: 29p
Intersecting D-Branes on Shift Z2 x Z2 Orientifolds
We investigate Z2 x Z2 orientifolds with group actions involving shifts. A
complete classification of possible geometries is presented where also previous
work by other authors is included in a unified framework from an intersecting
D-brane perspective. In particular, we show that the additional shifts not only
determine the topology of the orbifold but also independently the presence of
orientifold planes. In the second part, we work out in detail a basis of
homological three cycles on shift Z2 x Z2 orientifolds and construct all
possible fractional D-branes including rigid ones. A Pati-Salam type model with
no open-string moduli in the visible sector is presented.Comment: 36 pages, 4 figures, refs. adde
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