6,005 research outputs found
Revisiting spin alignment of heavy mesons in its inclusive production
In the heavy quark limit inclusive production rate of a heavy meson can be
factorized, in which the nonperturbative effect related to the heavy meson can
be characterized by matrix elements defined in the heavy quark effective
theory. Using this factorization, predictions for the full spin density matrix
of a spin-1 and spin-2 meson can be obtained and they are characterized only by
one coefficient representing the nonperturbative effect. Predictions for spin-1
heavy meson are compared with experiment performed at colliders in the
energy range from GeV to GeV, a complete agreement
is found for - and -meson. For meson, our prediction suffers
a large correction, as indicated by experimental data. There exists another
approach by taking heavy mesons as bound systems, in which the total angular
momentum of the light degrees of freedom is 1/2 and 3/2 for spin-1 and spin-2
meson respectively, then the diagonal parts of spin density matrices can be
obtained. However, there are distinct differences in the predictions from the
two approaches and they are discussed in detail.Comment: 14 pages with one figur
Inclusive CP Asymmetries in Semileptonic Decays of B Mesons
We estimate the sensitivity of single lepton CP violation measurements with
respect to that of traditional di-lepton measurements. We find that the
sensitivity of the single lepton method is better than that of the di-lepton
method. The achievable sensitivity with the currently available data is already
in the range relevant to standard model predictions. We also give general
expressions for inclusive decay time distributions on where the
other is not measured, which will be used to obtain time dependent
asymmetries. The expression is of general use whenever one deals with inclusive
time-dependent as well as time-integrated measurements in where the final state of the other is not reconstructed or
when only the time difference is measured.Comment: 7 pages, 1 figure. Two references added, and a few typos correcte
Comprehensive Two-Point Analyses of Weak Gravitational Lensing Surveys
We present a framework for analyzing weak gravitational lensing survey data,
including lensing and source-density observables, plus spectroscopic redshift
calibration data. All two-point observables are predicted in terms of
parameters of a perturbed Robertson-Walker metric, making the framework
independent of the models for gravity, dark energy, or galaxy properties. For
Gaussian fluctuations the 2-point model determines the survey likelihood
function and allows Fisher-matrix forecasting. The framework includes nuisance
terms for the major systematic errors: shear measurement errors, magnification
bias and redshift calibration errors, intrinsic galaxy alignments, and
inaccurate theoretical predictions. We propose flexible parameterizations of
the many nuisance parameters related to galaxy bias and intrinsic alignment.
For the first time we can integrate many different observables and systematic
errors into a single analysis. As a first application of this framework, we
demonstrate that: uncertainties in power-spectrum theory cause very minor
degradation to cosmological information content; nearly all useful information
(excepting baryon oscillations) is extracted with ~3 bins per decade of angular
scale; and the rate at which galaxy bias varies with redshift substantially
influences the strength of cosmological inference. The framework will permit
careful study of the interplay between numerous observables, systematic errors,
and spectroscopic calibration data for large weak-lensing surveys.Comment: submitted to Ap
Poly[diaquadi-μ 4-citrato-trizinc(II)]
The title compound, [Zn3(C6H5O7)2(H2O)2]n, is a polymer in which the repeating unit contains three zinc atoms, two hepta-dentate Hcit ligands (Hcit = citric acid trianion) and two coordinated water molecules, only half of which are independent due to one of the metal atoms lying on a centre of symmetry. The two independent cations both exhibit an octahedral geometry, but the way in which they are coordinate are different; while the Zn atom in a general position is bound to three Hcit ligands and one water molecule, the one at the centre of symmetry is coordinated by six O atoms from two symmetry-related Hcit ligands through the (protonated) hydroxyl and carboxylate groups. The three carboxylate groups coordinate to the Zn centres in three different ways, viz. chelating, bridging and a mixture of both, in an unusual coordination mode for citrate. The result is a two-dimensional structure parallel to (010), built up by a square-grid motif. Intermolecular O—H⋯O hydrogen bonds are present in the crystal structur
Noisy weak-lensing convergence peak statistics near clusters of galaxies and beyond
Taking into account noise from intrinsic ellipticities of source galaxies, in
this paper, we study the peak statistics in weak-lensing convergence maps
around clusters of galaxies and beyond. We emphasize how the noise peak
statistics is affected by the density distribution of nearby clusters, and also
how cluster-peak signals are changed by the existence of noise. These are the
important aspects to be understood thoroughly in weak-lensing analyses for
individual clusters as well as in cosmological applications of weak-lensing
cluster statistics. We adopt Gaussian smoothing with the smoothing scale
in our analyses. It is found that the noise peak
distribution near a cluster of galaxies depends sensitively on the density
profile of the cluster. For a cored isothermal cluster with the core radius
, the inner region with appears noisy containing on average
peaks with for and the true peak
height of the cluster , where denotes the convergence signal to
noise ratio. For a NFW cluster of the same mass and the same central , the
average number of peaks with within is . Thus a
high peak corresponding to the main cluster can be identified more cleanly in
the NFW case. In the outer region with , the number of high
noise peaks is considerably enhanced in comparison with that of the pure noise
case without the nearby cluster. (abridged)Comment: 10 figures, ApJ in pres
Optimal capture of non-Gaussianity in weak lensing surveys: power spectrum, bispectrum and halo counts
We compare the efficiency of weak lensing-selected galaxy clusters counts and
of the weak lensing bispectrum at capturing non-Gaussian features in the dark
matter distribution. We use the halo model to compute the weak lensing power
spectrum, the bispectrum and the expected number of detected clusters, and
derive constraints on cosmological parameters for a large, low systematic weak
lensing survey, by focusing on the - plane and on the dark
energy equation of state. We separate the power spectrum into the resolved and
the unresolved parts of the data, the resolved part being defined as detected
clusters, and the unresolved part as the rest of the field. We consider four
kinds of clusters counts, taking into account different amount of information :
signal-to-noise ratio peak counts; counts as a function of clusters' mass;
counts as a function of clusters' redshift; and counts as a function of
clusters' mass and redshift. We show that when combined with the power
spectrum, those four kinds of counts provide similar constraints, thus allowing
one to perform the most direct counts, signal-to-noise peaks counts, and get
percent level constraints on cosmological parameters. We show that the weak
lensing bispectrum gives constraints comparable to those given by the power
spectrum and captures non-Gaussian features as well as clusters counts, its
combination with the power spectrum giving errors on cosmological parameters
that are similar to, if not marginally smaller than, those obtained when
combining the power spectrum with cluster counts. We finally note that in order
to reach its potential, the weak lensing bispectrum must be computed using all
triangle configurations, as equilateral triangles alone do not provide useful
information.Comment: Matches ApJ-accepted versio
Distance, Growth Factor, and Dark Energy Constraints from Photometric Baryon Acoustic Oscillation and Weak Lensing Measurements
Baryon acoustic oscillations (BAOs) and weak lensing (WL) are complementary
probes of cosmology. We explore the distance and growth factor measurements
from photometric BAO and WL techniques and investigate the roles of the
distance and growth factor in constraining dark energy. We find for WL that the
growth factor has a great impact on dark energy constraints but is much less
powerful than the distance. Dark energy constraints from WL are concentrated in
considerably fewer distance eigenmodes than those from BAO, with the largest
contributions from modes that are sensitive to the absolute distance. Both
techniques have some well determined distance eigenmodes that are not very
sensitive to the dark energy equation of state parameters w_0 and w_a,
suggesting that they can accommodate additional parameters for dark energy and
for the control of systematic uncertainties. A joint analysis of BAO and WL is
far more powerful than either technique alone, and the resulting constraints on
the distance and growth factor will be useful for distinguishing dark energy
and modified gravity models. The Large Synoptic Survey Telescope (LSST) will
yield both WL and angular BAO over a sample of several billion galaxies. Joint
LSST BAO and WL can yield 0.5% level precision on ten comoving distances evenly
spaced in log(1+z) between redshift 0.3 and 3 with cosmic microwave background
priors from Planck. In addition, since the angular diameter distance, which
directly affects the observables, is linked to the comoving distance solely by
the curvature radius in the Friedmann-Robertson-Walker metric solution, LSST
can achieve a pure metric constraint of 0.017 on the mean curvature parameter
Omega_k of the universe simultaneously with the constraints on the comoving
distances.Comment: 15 pages, 9 figures, details and references added, ApJ accepte
Characterizing and Propagating Modeling Uncertainties in Photometrically-Derived Redshift Distributions
The uncertainty in the redshift distributions of galaxies has a significant
potential impact on the cosmological parameter values inferred from multi-band
imaging surveys. The accuracy of the photometric redshifts measured in these
surveys depends not only on the quality of the flux data, but also on a number
of modeling assumptions that enter into both the training set and SED fitting
methods of photometric redshift estimation. In this work we focus on the
latter, considering two types of modeling uncertainties: uncertainties in the
SED template set and uncertainties in the magnitude and type priors used in a
Bayesian photometric redshift estimation method. We find that SED template
selection effects dominate over magnitude prior errors. We introduce a method
for parameterizing the resulting ignorance of the redshift distributions, and
for propagating these uncertainties to uncertainties in cosmological
parameters.Comment: 13 pages, 12 figures, version published in Ap
An all-electric single-molecule hybridisation detector for short DNA fragments
In combining DNA nanotechnology and high-bandwidth single-molecule detection in nanopipettes, we demonstrate an all-electric, label-free hybridisation sensor for short DNA sequences (< 100 nt). Such short fragments are known to occur as circulating cell-free DNA in various bodily fluids, such as blood plasma and saliva, and have been identified as disease markers for cancer and infectious diseases. To this end, we use as a model system a 88-mer target from the RV1910c gene in Mycobacterium tuberculosis that is associated with antibiotic (isoniazid) resistance in TB. Upon binding to short probes attached to long carrier DNA, we show that resistive pulse sensing in nanopipettes is capable of identifying rather subtle structural differences, such as the hybridisation state of the probes, in a statistically robust manner. With significant potential towards multiplexing and high-throughput analysis, our study points towards a new, single-molecule DNA assay technology that is fast, easy to use and compatible with point of care environments
Optimal Surveys for Weak Lensing Tomography
Weak lensing surveys provide a powerful probe of dark energy through the
measurement of the mass distribution of the local Universe. A number of
ground-based and space-based surveys are being planned for this purpose. Here,
we study the optimal strategy for these future surveys using the joint
constraints on the equation of state parameter wn and its evolution wa as a
figure of merit by considering power spectrum tomography. For this purpose, we
first consider an `ideal' survey which is both wide and deep and exempt from
systematics. We find that such a survey has great potential for dark energy
studies, reaching one sigma precisions of 1% and 10% on the two parameters
respectively. We then study the relative impact of various limitations by
degrading this ideal survey. In particular, we consider the effect of sky
coverage, survey depth, shape measurements systematics, photometric redshifts
systematics and uncertainties in the non-linear power spectrum predictions. We
find that, for a given observing time, it is always advantageous to choose a
wide rather than a deep survey geometry. We also find that the dark energy
constraints from power spectrum tomography are robust to photometric redshift
errors and catastrophic failures, if a spectroscopic calibration sample of
10^4-10^5 galaxies is available. The impact of these systematics is small
compared to the limitations that come from potential uncertainties in the power
spectrum, due to shear measurement and theoretical errors. To help the planning
of future surveys, we summarize our results with comprehensive scaling
relations which avoid the need for full Fisher matrix calculations.Comment: Submitted to MNRAS. 10 pages, including 13 figures and 2 table
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