4,157 research outputs found
Electromagnetic Structure of the Z_c(3900)
The observation of the exotic quarkonium state Z_c(3900) by the BESIII and
Belle collaborations supports the concept of hadronic molecules. Charmonium
states interpreted as such molecules would be bound states of heavy particles
with small binding energies. This motivates their description using an
effective theory with contact interactions. In particular, we focus on the
electromagnetic structure of the charged state Z_c(3900). Using first
experimental results concerning spin and parity, we interpret it as an S-wave
molecule and calculate the form factors as well as charge and magnetic radii up
to next-to-leading order. We also present first numerical estimations of some
of these observables at leading order.Comment: 5 pages, 4 figures, final version to appear in Phys. Lett.
Universal Properties of the Four-Boson System in Two Dimensions
We consider the nonrelativistic four-boson system in two dimensions
interacting via a short-range attractive potential. For a weakly attractive
potential with one shallow two-body bound state with binding energy B_2, the
binding energies B_N of shallow N-body bound states are universal and thus do
not depend on the details of the interaction potential. We compute the
four-body binding energies in an effective quantum mechanics approach. There
are exactly two bound states: the ground state with B_4^(0)=197.3(1)B_2 and one
excited state with B_4^(1)=25.5(1)B_2. We compare our results to recent
predictions for N-body bound states with large N>>1.Comment: 7 pages, 1 ps figure, references and discussion added, final versio
New structures in the proton-antiproton system
In the most recent measurements of the reaction
by the BABAR collaboration, new structures have been found with unknown origin.
We examine a possible relation of the most distinct peak to the recently
observed . Alternatively, we analyse possible explanations due to
the nucleon and thresholds. The latter
could explain a periodicity found in the data
Effective Theory of 3H and 3He
We present a new perturbative expansion for pionless effective field theory
with Coulomb interactions in which at leading order the spin-singlet
nucleon-nucleon channels are taken in the unitarity limit. Presenting results
up to next-to-leading order for the Phillips line and the neutron-deuteron
doublet-channel phase shift, we find that a perturbative expansion in the
inverse 1S0 scattering lengths converges rapidly. Using a new systematic
treatment of the proton-proton sector that isolates the divergence due to
one-photon exchange, we renormalize the corresponding contribution to the
3H-3He binding energy splitting and demonstrate that the Coulomb force in
pionless EFT is a completely perturbative effect in the trinucleon bound-state
regime. In our new expansion, the leading order is exactly isospin-symmetric.
At next-to-leading order, we include isospin breaking via the Coulomb force and
two-body scattering lengths, and find for the energy splitting
(E_B(3He)-E_B(3H))^NLO = (-0.86 +/- 0.17) MeV.Comment: 37 pages, 14 figures, published versio
Nuclear Physics Around the Unitarity Limit
We argue that many features of the structure of nuclei emerge from a strictly
perturbative expansion around the unitarity limit, where the two-nucleon S
waves have bound states at zero energy. In this limit, the gross features of
states in the nuclear chart are correlated to only one dimensionful parameter,
which is related to the breaking of scale invariance to a discrete scaling
symmetry and set by the triton binding energy. Observables are moved to their
physical values by small, perturbative corrections, much like in descriptions
of the fine structure of atomic spectra. We provide evidence in favor of the
conjecture that light, and possibly heavier, nuclei are bound weakly enough to
be insensitive to the details of the interactions but strongly enough to be
insensitive to the exact size of the two-nucleon system.Comment: 6 pages, 3 figures, published version, rewritten for clarit
Biochemische Serumparameter bei in Gefangenschaft gehaltenen Gazellen
Objective: This study aimed at comparing serum parameters of clinically healthy gazelles of Al Wabra Wildlife Preservation (AWWP), Qatar, with reference ranges of domestic and other wild ruminants, in order to gain, on the one hand, insight into the nutritional status of the animals, and, on the other hand, to establish reference ranges for the investigated species. Material and methods: Serum biochemistry parameters and mineral levels were measured in 250 clinically healthy individuals of the species Soemmering's gazelle (Gazella soemmerringii), Speke's gazelle (Gazella spekei), Dorcas gazelle (Gazella dorcas), Saudi gazelle (Gazella saudiya), Mountain gazelle (Gazella gazella), Arabian goitered gazelle (Gazella subgutturosa marica) and Chinkara Pakistani gazelle (Gazella benetti). Results: With respect to the nutritional status, the supplementation with trace elements (selenium, copper, zinc, iron) was adequate at AWWP according to measured serum levels. In contrast, serum levels of phosphorus, total protein and albumin indicated a suboptimal feeding situation, most likely due to the low quality of the roughage available in the region. The levels of sodium, potassium, calcium, magnesium, choride, triglycerides, cholesterol, creatinine, ALT- as well as GGT avtivity were -as in other wild ruminants-within the reference range of domestic ruminants, which therefore should be applicable to ruminants in general. The contents of glucose, blood urea nitrogen, creatine kinase and ALP, in contrast, seem to be generally elevated in wild ruminants. While other wild ruminants display an AST activity comparable to those of domestic ruminants, gazelles of both this and other studies had elevated values of this enzyme. Conclusion and clinical relevance: These peculiarities need to be accounted for when interpreting blood values
Evaluating uniform manifold approximation and projection for dimension reduction and visualization of polinsar features
In this paper, the nonlinear dimension reduction algorithm Uniform Manifold Approximation and Projection (UMAP) is investigated to visualize information contained in high dimensional feature representations of Polarimetric Interferometric Synthetic Aperture Radar (PolInSAR) data. Based on polarimetric parameters, target decomposition methods and interferometric coherences a wide range of features is extracted that spans the high dimensional feature space. UMAP is applied to determine a representation of the data in 2D and 3D euclidean space, preserving local and global structures of the data and still suited for classification. The performance of UMAP in terms of generating expressive visualizations is evaluated on PolInSAR data acquired by the F-SAR sensor and compared to that of Principal Component Analysis (PCA), Laplacian Eigenmaps (LE) and t-distributed Stochastic Neighbor embedding (t-SNE). For this purpose, a visual analysis of 2D embeddings is performed. In addition, a quantitative analysis is provided for evaluating the preservation of information in low dimensional representations with respect to separability of different land cover classes. The results show that UMAP exceeds the capability of PCA and LE in these regards and is competitive with t-SNE
Recent Developments in the Nuclear Many-Body Problem
The study of quantum chromodynamics (QCD) over the past quarter century has
had relatively little impact on the traditional approach to the low-energy
nuclear many-body problem. Recent developments are changing this situation. New
experimental capabilities and theoretical approaches are opening windows into
the richness of many-body phenomena in QCD. A common theme is the use of
effective field theory (EFT) methods, which exploit the separation of scales in
physical systems. At low energies, effective field theory can explain how
existing phenomenology emerges from QCD and how to refine it systematically.
More generally, the application of EFT methods to many-body problems promises
insight into the analytic structure of observables, the identification of new
expansion parameters, and a consistent organization of many-body corrections,
with reliable error estimates.Comment: 15 pages, 10 figures, plenary talk at the 11th Conference on Recent
Progress in Many-Body Theories (MB 11), Manchester, England, 9-13 Jul 200
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