9,415 research outputs found
A Small Cosmological Constant and Backreaction of Non-Finetuned Parameters
We include the backreaction on the warped geometry induced by non-finetuned
parameters in a two domain-wall set-up to obtain an exponentially small
Cosmological Constant . The mechanism to suppress the Cosmological
Constant involves one classical fine-tuning as compared to an infinity of
finetunings at the quantum level in standard D=4 field theory.Comment: 13 pages, minor corrections and references adde
Dark Energy Survey Year 1 Results: Multi-Probe Methodology and Simulated Likelihood Analyses
We present the methodology for and detail the implementation of the Dark Energy Survey (DES) 3x2pt DES Year 1 (Y1) analysis, which combines configuration-space two-point statistics from three different cosmological probes: cosmic shear, galaxy-galaxy lensing, and galaxy clustering, using data from the first year of DES observations. We have developed two independent modeling pipelines and describe the code validation process. We derive expressions for analytical real-space multi-probe covariances, and describe their validation with numerical simulations. We stress-test the inference pipelines in simulated likelihood analyses that vary 6-7 cosmology parameters plus 20 nuisance parameters and precisely resemble the analysis to be presented in the DES 3x2pt analysis paper, using a variety of simulated input data vectors with varying assumptions.
We find that any disagreement between pipelines leads to changes in assigned likelihood Δχ^2 ≤ 0.045 with respect to the statistical error of the DES Y1 data vector. We also find that angular binning and survey mask do not impact our analytic covariance at a significant level. We determine lower bounds on scales used for analysis of galaxy clustering (8 Mpc h^(−1)) and galaxy-galaxy lensing (12 Mpc h^(−1)) such that the impact of modeling uncertainties in the non-linear regime is well below statistical errors, and show that our analysis choices are robust against a variety of systematics. These tests demonstrate that we have a robust analysis pipeline that yields unbiased cosmological parameter inferences for the flagship 3x2pt DES Y1 analysis. We emphasize that the level of independent code development and subsequent code comparison as demonstrated in this paper is necessary to produce credible constraints from increasingly complex multi-probe analyses of current data
Breakdown of Angular Momentum Selection Rules in High Pressure Optical Pumping Experiments
We present measurements, using two complementary methods, of the breakdown of
atomic angular momentum selection rules in He-broadened Rb vapor. Atomic dark
states are rendered weakly absorbing due to fine-structure mixing during Rb-He
collisions. The effect substantially increases the photon demand for optical
pumping of dense vapors
Large-Amplitude, Pair-Creating Oscillations in Pulsar and Black Hole Magnetospheres
A time-dependent model for pair creation in a pulsar magnetosphere is
developed. It is argued that the parallel electric field that develops in a
charge-starved region (a gap) of a pulsar magnetosphere oscillates with large
amplitude. Electrons and positrons are accelerated periodically and the
amplitude of the oscillations is assumed large enough to cause creation of
upgoing and downgoing pairs at different phases of the oscillation. With a
charge-starved initial condition, we find that the oscillations result in
bursts of pair creation in which the pair density rises exponentially with
time. The pair density saturates at , where is the parallel electric field in the
charge-starved initial state, and is the Lorentz factor for
effec tive pair creation. The frequency of oscillations following the pair
creation burst is given roughly by . A positive feedback keeps the system stable, such that the average pair
creation rate balances the loss rate due to pairs escaping the magnetosphere.Comment: 21 pages, 6 figures, ApJ submitte
A multielement probe for coincident temperature and pressure measurements
Small, multielement probes are described which measure total pressure and temperature coincidentally at one or several points in gas stream
Electroweak Fermion-loop Contributions to the Muon Anomalous Magnetic Moment
The two-loop electroweak corrections to the anomalous magnetic moment of the
muon, generated by fermionic loops, are calculated. An interesting role of the
top quark in the anomaly cancellation is observed. New corrections, including
terms of order , are computed and a class of diagrams
previously thought to vanish are found to be important. The total fermionic
correction is which decreases the electroweak
effects on , predicted from one-loop calculations, by 12\%. We give an
updated theoretical prediction for of the muon.Comment: Corrected versio
Are the singularities stable?
The spacetime singularities play a useful role in gravitational theories by
distinguishing physical solutions from non-physical ones. The problem, we
studying in this paper is: are these singularities stable? To answer this
question, we have analyzed the general problem of stability of the family of
the static spherically symmetric solutions of the standard Einstein-Maxwell
model coupled to an extra free massless scalar field. We have obtained the
equations for the axial and polar perturbations. The stability against axial
perturbations has been proven.Comment: 13 pages, LaTeX, no figure
Clustering of vacancy defects in high-purity semi-insulating SiC
Positron lifetime spectroscopy was used to study native vacancy defects in
semi-insulating silicon carbide. The material is shown to contain (i) vacancy
clusters consisting of 4--5 missing atoms and (ii) Si vacancy related
negatively charged defects. The total open volume bound to the clusters
anticorrelates with the electrical resistivity both in as-grown and annealed
material. Our results suggest that Si vacancy related complexes compensate
electrically the as-grown material, but migrate to increase the size of the
clusters during annealing, leading to loss of resistivity.Comment: 8 pages, 5 figure
Direct strain and elastic energy evaluation in rolled-up semiconductor tubes by x-ray micro-diffraction
We depict the use of x-ray diffraction as a tool to directly probe the strain
status in rolled-up semiconductor tubes. By employing continuum elasticity
theory and a simple model we are able to simulate quantitatively the strain
relaxation in perfect crystalline III-V semiconductor bi- and multilayers as
well as in rolled-up layers with dislocations. The reduction in the local
elastic energy is evaluated for each case. Limitations of the technique and
theoretical model are discussed in detail.Comment: 32 pages (single column), 9 figures, 39 reference
Thermophysical and chemical characterization of charring ablative materials Final report
Thermophysical and chemical properties of charring ablative material
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