1,788 research outputs found
Stabilizing All Geometric Moduli in Heterotic Calabi-Yau Vacua
We propose a scenario to stabilize all geometric moduli - that is, the
complex structure, Kahler moduli and the dilaton - in smooth heterotic
Calabi-Yau compactifications without Neveu-Schwarz three-form flux. This is
accomplished using the gauge bundle required in any heterotic compactification,
whose perturbative effects on the moduli are combined with non-perturbative
corrections. We argue that, for appropriate gauge bundles, all complex
structure and a large number of other moduli can be perturbatively stabilized -
in the most restrictive case, leaving only one combination of Kahler moduli and
the dilaton as a flat direction. At this stage, the remaining moduli space
consists of Minkowski vacua. That is, the perturbative superpotential vanishes
in the vacuum without the necessity to fine-tune flux. Finally, we incorporate
non-perturbative effects such as gaugino condensation and/or instantons. These
are strongly constrained by the anomalous U(1) symmetries which arise from the
required bundle constructions. We present a specific example, with a consistent
choice of non-perturbative effects, where all remaining flat directions are
stabilized in an AdS vacuum.Comment: 24 pages, 2 figure
Size-Dependent Variability in Flow and Viscoelastic Behavior of Levan Produced by Gluconobacter albidus TMW 2.1191
Levan is a fructan-type exopolysaccharide which is produced by many microbes from sucrose via extracellular levansucrases. The hydrocolloid properties of levan depend on its molecular weight, while it is unknown why and to what extent levan is functionally diverse depending on ist size. The aim of our study was to gain deeper insight into the size-dependent functional variability of levan. For this purpose, levans of different sizes were produced using the water kefir isolate Gluconobacter albidus TMW 2.1191 and subsequently rheologically characterized. Three levan types could be identified, which are similarly branched, but differ significantly in their molecular size and rheological properties. The smallest levan (10 Da) produced at pH ≥ 4.5 were shear-thinning, and the levan produced at pH 5.0 showed a gel-like behavior at 5% (w/v). A third (intermediate) levan variant was obtained through production in buffers at pH 4.0 and exhibited the properties of a viscoelastic fluid up to concentrations of 15% (w/v). Our study reveals that the rheological properties of levan are determined by its size and polydispersity, rather than by the amount of levan used or the structural composition
Light-cone distribution amplitudes of the baryon octet
We present results of the first ab initio lattice QCD calculation of the
normalization constants and first moments of the leading twist distribution
amplitudes of the full baryon octet, corresponding to the small transverse
distance limit of the associated S-wave light-cone wave functions. The P-wave
(higher twist) normalization constants are evaluated as well. The calculation
is done using flavors of dynamical (clover) fermions on lattices of
different volumes and pion masses down to 222 MeV. Significant SU(3) flavor
symmetry violation effects in the shape of the distribution amplitudes are
observed.Comment: Update to the version published in JHE
Stability Walls in Heterotic Theories
We study the sub-structure of the heterotic Kahler moduli space due to the
presence of non-Abelian internal gauge fields from the perspective of the
four-dimensional effective theory. Internal gauge fields can be supersymmetric
in some regions of the Kahler moduli space but break supersymmetry in others.
In the context of the four-dimensional theory, we investigate what happens when
the Kahler moduli are changed from the supersymmetric to the non-supersymmetric
region. Our results provide a low-energy description of supersymmetry breaking
by internal gauge fields as well as a physical picture for the mathematical
notion of bundle stability. Specifically, we find that at the transition
between the two regions an additional anomalous U(1) symmetry appears under
which some of the states in the low-energy theory acquire charges. We compute
the associated D-term contribution to the four-dimensional potential which
contains a Kahler-moduli dependent Fayet-Iliopoulos term and contributions from
the charged states. We show that this D-term correctly reproduces the expected
physics. Several mathematical conclusions concerning vector bundle stability
are drawn from our arguments. We also discuss possible physical applications of
our results to heterotic model building and moduli stabilization.Comment: 37 pages, 4 figure
Stabilizing the Complex Structure in Heterotic Calabi-Yau Vacua
In this paper, we show that the presence of gauge fields in heterotic
Calabi-Yau compacitifications causes the stabilisation of some, or all, of the
complex structure moduli of the Calabi-Yau manifold while maintaining a
Minkowski vacuum. Certain deformations of the Calabi-Yau complex structure,
with all other moduli held fixed, can lead to the gauge bundle becoming
non-holomorphic and, hence, non-supersymmetric. This leads to an F-term
potential which stabilizes the corresponding complex structure moduli. We use
10- and 4-dimensional field theory arguments as well as a derivation based
purely on algebraic geometry to show that this picture is indeed correct. An
explicit example is presented in which a large subset of complex structure
moduli is fixed. We demonstrate that this type of theory can serve as the
hidden sector in heterotic vacua and can co-exist with realistic particle
physics.Comment: 17 pages, Late
Heterotic Line Bundle Standard Models
In a previous publication, arXiv:1106.4804, we have found 200 models from
heterotic Calabi-Yau compactifications with line bundles, which lead to
standard models after taking appropriate quotients by a discrete symmetry and
introducing Wilson lines. In this paper, we construct the resulting standard
models explicitly, compute their spectrum including Higgs multiplets, and
analyze some of their basic properties. After removing redundancies we find
about 400 downstairs models, each with the precise matter spectrum of the
supersymmetric standard model, with one, two or three pairs of Higgs doublets
and no exotics of any kind. In addition to the standard model gauge group, up
to four Green-Schwarz anomalous U(1) symmetries are present in these models,
which constrain the allowed operators in the four-dimensional effective
supergravity. The vector bosons associated to these anomalous U(1) symmetries
are massive. We explicitly compute the spectrum of allowed operators for each
model and present the results, together with the defining data of the models,
in a database of standard models accessible at
http://www-thphys.physics.ox.ac.uk/projects/CalabiYau/linebundlemodels/index.html.
Based on these results we analyze elementary phenomenological properties. For
example, for about 200 models all dimension four and five proton decay
violating operators are forbidden by the additional U(1) symmetries.Comment: 55 pages, Latex, 3 pdf figure
G-structures and Domain Walls in Heterotic Theories
We consider heterotic string solutions based on a warped product of a
four-dimensional domain wall and a six-dimensional internal manifold,
preserving two supercharges. The constraints on the internal manifolds with
SU(3) structure are derived. They are found to be generalized half-flat
manifolds with a particular pattern of torsion classes and they include
half-flat manifolds and Strominger's complex non-Kahler manifolds as special
cases. We also verify that previous heterotic compactifications on half-flat
mirror manifolds are based on this class of solutions.Comment: 29 pages, reference added, typos correcte
Inhibition of Notch2 by Numb/Numblike controls myocardial compaction in the heart
Aims The ventricular wall of the heart is composed of trabeculated and compact layers, which are separated by yet unknown processes during embryonic development. Here, we wanted to explore the role of Notch2 and Numb/Numblike for myocardial trabeculation and compaction. Methods and results We found that Notch2 activity is specifically down-regulated in the compact layer during cardiac development in the mouse. The biological role of Notch2 down-regulation was investigated by the expression of constitutively active Notch2 in the myocardium of transgenic mice, resulting in hypertrabeculation, reduced compaction, and ventricular septum defects. To disclose the mechanism that inhibited Notch2 activity during the formation of myocardial layers, we analysed potential suppressors of Notch signalling. We unveiled that concomitant but not separate ablation of Numb and Numblike in the developing heart leads to increased Notch2 activity along with hypertrabeculation, reduced compaction, and ventricular septum defects, phenocopying effects gained by overexpression of constitutively active Notch2. Expression profiling revealed a strong up-regulation of Bmp10 in Numb/Numblike mutant hearts, which might also interfere with trabeculation and compaction. Conclusion This study identified potential novel roles of Numb/Numblike in regulating trabeculation and compaction by inhibiting Notch2 and Bmp10 signallin
Toward a fully cloudified mobile network infrastructure
Cloud computing enables the on-demand delivery of resources for a multitude of services and gives the opportunity for small agile companies to compete with large industries. In the telco world, cloud computing is currently mostly used by mobile network operators (MNO) for hosting non-critical support services and selling cloud services such as applications and data storage. MNOs are investigating the use of cloud computing to deliver key telecommunication services in the access and core networks. Without this, MNOs lose the opportunities of both combining this with over-the-top (OTT) and value-added services to their fundamental service offerings and leveraging cost-effective commodity hardware. Being able to leverage cloud computing technology effectively for the telco world is the focus of mobile cloud networking (MCN). This paper presents the key results of MCN integrated project that includes its architecture advancements, prototype implementation, and evaluation. Results show the efficiency and the simplicity that a MNO can deploy and manage the complete service lifecycle of fully cloudified, composed services that combine OTT/IT- and mobile-network-based services running on commodity hardware. The extensive performance evaluation of MCN using two key proof-of-concept scenarios that compose together many services to deliver novel converged elastic, on-demand mobile-based but innovative OTT services proves the feasibility of such fully virtualized deployments. Results show that it is beneficial to extend cloud computing to telco usage and run fully cloudified mobile-network-based systems with clear advantages and new service opportunities for MNOs and end-users
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