1,318 research outputs found
The scaling dimension of low lying Dirac eigenmodes and of the topological charge density
As a quantitative measure of localization, the inverse participation ratio of
low lying Dirac eigenmodes and topological charge density is calculated on
quenched lattices over a wide range of lattice spacings and volumes. Since
different topological objects (instantons, vortices, monopoles, and artifacts)
have different co-dimension, scaling analysis provides information on the
amount of each present and their correlation with the localization of low lying
eigenmodes.Comment: Lattice2004(topology), Fermilab, June 21 - 26, 2004; 3 pages, 3
figure
R Symmetries in the Landscape
In the landscape, states with symmetries at the classical level form a
distinct branch, with a potentially interesting phenomenology. Some preliminary
analyses suggested that the population of these states would be significantly
suppressed. We survey orientifolds of IIB theories compactified on Calabi-Yau
spaces based on vanishing polynomials in weighted projective spaces, and find
that the suppression is quite substantial. On the other hand, we find that a
R-parity is a common feature in the landscape. We discuss whether the
cosmological constant and proton decay or cosmology might select the low energy
branch. We include also some remarks on split supersymmetry.Comment: 13 page
Realistic D-Brane Models on Warped Throats: Fluxes, Hierarchies and Moduli Stabilization
We describe the construction of string theory models with semirealistic
spectrum in a sector of (anti) D3-branes located at an orbifold singularity at
the bottom of a highly warped throat geometry, which is a generalisation of the
Klebanov-Strassler deformed conifold. These models realise the Randall-Sundrum
proposal to naturally generate the Planck/electroweak hierarchy in a concrete
string theory embedding, and yielding interesting chiral open string spectra.
We describe examples with Standard Model gauge group (or left-right symmetric
extensions) and three families of SM fermions, with correct quantum numbers
including hypercharge. The dilaton and complex structure moduli of the geometry
are stabilised by the 3-form fluxes required to build the throat. We describe
diverse issues concerning the stabilisation of geometric Kahler moduli, like
blow-up modes of the orbifold singularities, via D term potentials and gauge
theory non-perturbative effects, like gaugino condensation. This local
geometry, once embedded in a full compactification, could give rise to models
with all moduli stabilised, and with the potential to lead to de Sitter vacua.
Issues of gauge unification, proton stability, supersymmetry breaking and
Yukawa couplings are also discussed.Comment: 46 pages, 13 figures (figures 3 and 13 corrected
Surveying Standard Model Flux Vacua on
We consider the SU(2)LxSU(2)R Standard Model brane embedding in an
orientifold of T6/Z2xZ2. Within defined limits, we construct all such Standard
Model brane embeddings and determine the relative number of flux vacua for each
construction. Supersymmetry preserving brane recombination in the hidden sector
enables us to identify many solutions with high flux. We discuss in detail the
phenomenology of one model which is likely to dominate the counting of vacua.
While Kahler moduli stabilization remains to be fully understood, we define the
criteria necessary for generic constructions to have fixed moduli.Comment: 30 pages, LaTeX, v2: added reference
Photocatalysed (Meth)acrylate Polymerization by (Antimony-Doped) Tin Oxide Nanoparticles and Photoconduction of Their Crosslinked Polymer Nanoparticle Composites
In the absence of another (photo)radical initiator Sb:SnO 2 nanoparticles (0 ≤ Sb ≤ 13 at %) photocatalyze during irradiation with UV light the radical polymerization of (meth)acrylate monomers. When cured hard and transparent (>98%) films with a low haze (<1%) are required, when these particles are grafted in advance with 3-methacryloxypropyltrimethoxysilane (MPS) and doped with Sb. Public knowledge about the photocatalytic properties of Sb:SnO 2 nanoparticles is hardly available. Therefore, the influence of particle concentration, surface groups, and Sb doping on the rate of C=C (meth)acrylate bond polymerization was determined with aid of real-time FT-IR spectroscopy. By using a wavelength of irradiation with a narrow bandgab (315 ± 5 nm) the influence of these factors on the quantum yield (Φ) and on polymer and particle network structure formation was determined. It is shown that Sb doping and MPS grafting of the particles lowers Φ. MPS grafting of the particles also influences the structure of the polymer network formed. Without Sb doping of these particles unwanted, photocatalytic side reactions occur. It is also shown that cured MPS-Sb:SnO 2 /(meth)acrylate nanocomposites have photoconduction properties even when the particle concentration is as low as 1 vol.%. The results suggest that the Sb:SnO 2 (Sb > 0 at %) nanoparticles can be attractive fillers for other photocatalytic applications photorefractive materials, optoelectronic devices and sensors
Linked randomised controlled trials of face-to-face and electronic brief intervention methods to prevent alcohol related harm in young people aged 14–17 years presenting to Emergency Departments (SIPS junior)
Background: Alcohol is a major global threat to public health. Although the main burden of chronic alcohol-related disease is in adults, its foundations often lie in adolescence. Alcohol consumption and related harm increase steeply from the age of 12 until 20 years. Several trials focusing upon young people have reported significant positive effects of brief interventions on a range of alcohol consumption outcomes. A recent review of reviews also suggests that electronic brief interventions (eBIs) using internet and smartphone technologies may markedly reduce alcohol consumption compared with minimal or no intervention controls.
Interventions that target non-drinking youth are known to delay the onset of drinking behaviours. Web based alcohol interventions for adolescents also demonstrate significantly greater reductions in consumption and harm among ‘high-risk’ drinkers; however changes in risk status at follow-up for non-drinkers or low-risk
drinkers have not been assessed in controlled trials of brief alcohol interventions
Racetrack Inflation
We develop a model of eternal topological inflation using a racetrack
potential within the context of type IIB string theory with KKLT volume
stabilization. The inflaton field is the imaginary part of the K\"ahler
structure modulus, which is an axion-like field in the 4D effective field
theory. This model does not require moving branes, and in this sense it is
simpler than other models of string theory inflation. Contrary to
single-exponential models, the structure of the potential in this example
allows for the existence of saddle points between two degenerate local minima
for which the slow-roll conditions can be satisfied in a particular range of
parameter space. We conjecture that this type of inflation should be present in
more general realizations of the modular landscape. We also consider
`irrational' models having a dense set of minima, and discuss their possible
relevance for the cosmological constant problem.Comment: 23 pages 7 figures. The final version with minor modifications, to
appear in JHE
Warped Tachyonic Inflation in Type IIB Flux Compactifications and the Open-String Completeness Conjecture
We consider a cosmological scenario within the KKLT framework for moduli
stabilization in string theory. The universal open string tachyon of decaying
non-BPS D-brane configurations is proposed to drive eternal topological
inflation. Flux-induced `warping' can provide the small slow-roll parameters
needed for successful inflation. Constraints on the parameter space leading to
sufficient number of e-folds, exit from inflation, density perturbations and
stabilization of the Kahler modulus are investigated. The conditions are
difficult to satisfy in Klebanov-Strassler throats but can be satisfied in T^3
fibrations and other generic Calabi-Yau manifolds. This requires large volume
and magnetic fluxes on the D-brane. The end of inflation may or may not lead to
cosmic strings depending on the original non-BPS configuration. A careful
investigation of initial conditions leading to a phenomenologically viable
model for inflation is carried out. The initial conditions are chosen on the
basis of Sen's open string completeness conjecture. We find time symmetrical
bounce solutions without initial singularities for k=1 FRW models which are
correlated with an inflationary period. Singular big-bang/big-crunch solutions
also exist but do not lead to inflation. There is an intriguing correlation
between having an inflationary universe in 4 dimensions and 6 compact
dimensions or a big-crunch singularity and decompactification.Comment: 43 pages, 9 figures. v3: Typos correcte
Information, disturbance and Hamiltonian quantum feedback control
We consider separating the problem of designing Hamiltonian quantum feedback
control algorithms into a measurement (estimation) strategy and a feedback
(control) strategy, and consider optimizing desirable properties of each under
the minimal constraint that the available strength of both is limited. This
motivates concepts of information extraction and disturbance which are distinct
from those usually considered in quantum information theory. Using these
concepts we identify an information trade-off in quantum feedback control.Comment: 13 pages, multicol Revtex, 2 eps figure
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