393 research outputs found
The axion-baryon coupling in SU(3) heavy baryon chiral perturbation theory
In the past, the axion-nucleon coupling has been calculated in the framework
of SU(2) heavy baryon chiral perturbation theory up to third order in the
chiral power counting. Here, we extend these earlier studies to the case of
heavy baryon chiral perturbation theory with SU(3) flavor symmetry and derive
the axion coupling to the full SU(3) baryon octet, showing that the axion also
significantly couples to hyperons. As studies on dense nuclear matter suggest
the possible existence of hyperons in stellar objects such as neutron stars,
our results should have phenomenological implications related to the so-called
axion window.Comment: 45 pages, 1 figur
Pion axioproduction: The Delta resonance contribution
The process of pion axioproduction, , with an intermediate
resonance is analyzed using baryon chiral parturbation theory. The
resonance is included in two ways: First, deriving the -vertices, the axion is brought into contact with the resonance, and, second,
taking the results of elastic scattering including the , it is
implicitly included in the form of a pion rescattering diagram. As a result,
the partial wave cross section of axion-nucleon scattering shows an enhancement
in the energy region around the resonance. Because of the isospin
breaking, the enhancement is not as pronounced as previously anticipated.
However, since the isospin breaking here is much milder than that for usual
hadronic processes, novel axion search experiments might still exploit this
effect.Comment: 13 pages, 5 figure
Precision calculation of the axion-nucleon coupling in chiral perturbation theory
We derive the axion-nucleon interaction Lagrangian in heavy baryon chiral
perturbation theory up to next-to-next-to-leading order. The effective
axion-nucleon coupling is calculated to a few percent accuracy.Comment: 20 page
DESY NanoLab
The DESY NanoLab is a facility providing access to nano-characterization, nano-structuring and nano-synthesis techniques which are complementary to the advanced X-ray techniques available at DESY’s light sources. It comprises state-of-the art scanning probe microscopy and focused ion beam manufacturing, as well as surface sensitive spectroscopy techniques for chemical analysis. Specialized laboratory x-ray diffraction setups are available for a successful sample pre-characterization before the precious synchrotron beamtimes. Future upgrades will include as well characterization of magnetic properties
-dependence of light nuclei and nucleosynthesis
We investigate the impact of the QCD vacuum at nonzero on the
properties of light nuclei, Big Bang nucleosynthesis, and stellar
nucleosynthesis. Our analysis starts with a calculation of the
-dependence of the neutron-proton mass difference and neutron decay
using chiral perturbation theory. We then discuss the -dependence of
the nucleon-nucleon interaction using a one-boson-exchange model and compute
the properties of the two-nucleon system. Using the universal properties of
four-component fermions at large scattering length, we then deduce the binding
energies of the three-nucleon and four-nucleon systems. Based on these results,
we discuss the implications for primordial abundances of light nuclei, the
production of nuclei in stellar environments, and implications for an anthropic
view of the universe.Comment: 20 pages, 9 figure
QCD -vacuum energy and axion properties
At low energies, the strong interaction is governed by the Goldstone bosons
associated with the spontaneous chiral symmetry breaking, which can be
systematically described by chiral perturbation theory. In this paper, we apply
this theory to study the -vacuum energy density and hence the QCD axion
potential up to next-to-leading order with non-degenerate quark masses. By
setting , we then derive the axion mass, self-coupling, topological
susceptibility and the normalized fourth cumulant both analytically and
numerically, taking the strong isospin breaking effects into account. In
addition, the model-independent part of the axion-photon coupling, which is
important for axion search experiments, is also extracted from the chiral
Lagrangian supplemented with the anomalous terms up to .Comment: 22 pages, 1 figure, 2 tables; Version to appear in JHE
Model selection based on combined penalties for biomarker identification
The growing role of targeted medicine has led to an increased focus on the development of actionable biomarkers. Current penalized selection methods that are used to identify biomarker panels for classification in high-dimensional data, however, often result in highly complex panels that need careful pruning for practical use. In the framework of regularization methods, a penalty that is a weighted sum of the L1 and L0 norm has been proposed to account for the complexity of the resulting model. In practice, the limitation of this penalty is that the objective function is non-convex, non-smooth, the optimization is computationally intensive and the application to high-dimensional settings is challenging. In this paper, we propose a stepwise forward variable selection method which combines the L0 with L1 or L2 norms. The penalized likelihood criterion that is used in the stepwise selection procedure results in more parsimonious models, keeping only the most relevant features. Simulation results and a real application show that our approach exhibits a comparable performance with common selection methods with respect to the prediction performance while minimizing the number of variables in the selected model resulting in a more parsimonious model as desired
A Bayesian model to estimate the cutoff and the clinical utility of a biomarker assay
To enable targeted therapies and enhance medical decision-making, biomarkers are increasingly used as screening and diagnostic tests. When using quantitative biomarkers for classification purposes, this often implies that an appropriate cutoff for the biomarker has to be determined and its clinical utility must be assessed. In the context of drug development, it is of interest how the probability of response changes with increasing values of the biomarker. Unlike sensitivity and specificity, predictive values are functions of the accuracy of the test, depend on the prevalence of the disease and therefore are a useful tool in this setting. In this paper, we propose a Bayesian method to not only estimate the cutoff value using the negative and positive predictive values, but also estimate the uncertainty around this estimate. Using Bayesian inference allows us to incorporate prior information, and obtain posterior estimates and credible intervals for the cut-off and associated predictive values. The performance of the Bayesian approach is compared with alternative methods via simulation studies of bias, interval coverage and width and illustrations on real data with binary and time-to-event outcomes are provided
CRISPR/Cas12a Multiplex Genome Editing of <i>Saccharomyces cerevisiae </i>and the Creation of Yeast Pixel Art
Single Alloy Nanoparticle X-Ray Imaging during a Catalytic Reaction
The imaging of active nanoparticles represents a milestone in decoding
heterogeneous catalysts dynamics. We report the facet resolved, surface strain
state of a single PtRh alloy nanoparticle on SrTiO3 determined by coherent
x-ray diffraction imaging under catalytic reaction conditions. Density
functional theory calculations allow us to correlate the facet surface strain
state to its reaction environment dependent chemical composition. We find that
the initially Pt terminated nanoparticle surface gets Rh enriched under CO
oxidation reaction conditions. The local composition is facet orientation
dependent and the Rh enrichment is non-reversible under subsequent CO
reduction. Tracking facet resolved strain and composition under operando
conditions is crucial for a rational design of more efficient heterogeneous
catalysts with tailored activity, selectivity and lifetime.Comment: 15 pages, 4 figures, 32 reference
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