Bethe-Salpeter equation for doubly heavy baryons in the covariant instantaneous approximation

In the heavy quark limit, a doubly heavy baryon is regarded as composed of a heavy diquark and a light quark. We establish the Bethe-Salpeter (BS) equations for the heavy diquarks and the doubly heavy baryons, respectively, to leading order in a $1/m_{Q}$ expansion. The BS equations are solved numerically under the covariant instantaneous approximation with the kernels containing scalar confinement and one-gluon-exchange terms. The masses for the heavy diquarks and the doubly heavy baryons are obtained and the non-leptonic decay widths for the doubly heavy baryons emitting a pseudo-scalar meson are calculated within the model.Comment: Corrections to the text, two references added, version accepted for publication in Physical Review

Testing Non-local Nucleon-Nucleon Interactions in the Four-Nucleon Systems

The Faddeev-Yakubovski equations are solved in configuration space for the $\alpha$-particle and n-$^3$H continuum states. We test the ability of nonlocal nucleon-nucleon interaction models to describe 3N and 4N systems.Comment: 16 pages, 6 figure

Human visual sampling processes - A simulation validation study

Pilots and flight simulator used in study of human visual sampling stud

The importance of few-nucleon physics at low energy

This manuscript originated from the discussion at the workshop on the "Future of Few-body Low Energy Experimental Physics" (FFLEEP), which was held at the University of Trento on December 4-7, 2002 and has been written in its present form on March 19, 2003. It illustrates a selection of theoretical advancements in the nuclear few-body problem, including two- and many-nucleon interactions, the three-nucleon bound and scattering system, the four-body problem, the A-body (A$>$4) problem, and fields of related interest, such as reactions of astrophysical interest and few-neutron systems. Particular attention is called to the contradictory situation one experiences in this field: while theory is currently advancing and has the potential to inspire new experiments, the experimental activity is nevertheless rapidly phasing out. If such a trend will continue, advancements in this area will become critically difficult.Comment: 29 pages, 21 figures. Manuscript originated from the discussion at the workshop on the "Future of Few-body Low Energy Experimental Physics" (FFLEEP), University of Trento, December 4-7, 2002, written in its present form on March 19, 2003, circulated mainly among the participants to the FFLEEP workshop. Since the authors have been repeatedly solicited to make the manuscript accessible to a larger audience potentially interested in its scientific content, they have decided to post it on this archiv

Antiproton-Hydrogen annihilation at sub-kelvin temperatures

The main properties of the interaction of ultra low-energy antiprotons ($E\le10^{-6}$ a.u.) with atomic hydrogen are established. They include the elastic and inelastic cross sections and Protonium (Pn) formation spectrum. The inverse Auger process ($Pn+e \to H+\bar{p}$) is taken into account in the framework of an unitary coupled-channels model. The annihilation cross-section is found to be several times smaller than the predictions made by the black sphere absorption models. A family of $\bar{p}H$ nearthreshold metastable states is predicited. The dependence of Protonium formation probability on the position of such nearthreshold S-matrix singularities is analysed. An estimation for the $H\bar{H}$ annihilation cross section is obtained.Comment: latex.tar.gz file, 22 pages, 9 figure

Four-nucleon scattering: Ab initio calculations in momentum space

The four-body equations of Alt, Grassberger and Sandhas are solved for \nH scattering at energies below three-body breakup threshold using various realistic interactions including one derived from chiral perturbation theory. After partial wave decomposition the equations are three-variable integral equations that are solved numerically without any approximations beyond the usual discretization of continuum variables on a finite momentum mesh. Large number of two-, three- and four-nucleon partial waves are considered until the convergence of the observables is obtained. The total \nH cross section data in the resonance region is not described by the calculations which confirms previous findings by other groups. Nevertheless the numbers we get are slightly higher and closer to the data than previously found and depend on the choice of the two-nucleon potential. Correlations between the $A_y$ deficiency in \nd elastic scattering and the total \nH cross section are studied.Comment: Corrected Eq. (10

Deer reduce habitat quality for a woodland songbird: evidence from settlement patterns, demographic parameters, and body condition.

Understanding avian responses to ungulate-induced habitat modification is important because deer populations are increasing across much of temperate Europe and North America. Our experimental study examined whether habitat quality for Blackcaps (Sylvia atricapilla) in young woodland in eastern England was affected by deer, by comparing Blackcap behavior, abundance, and condition between paired plots (half of each pair protected from deer). The vegetation in each pair of plots was the same age. The Blackcap is an ideal model species for testing effects of deer on avian habitat quality because it is dependent on dense understory vegetation and is abundant throughout much of Europe. We compared timing of settlement, abundance, age structure (second-year vs. after-second-year), and phenotypic quality (measured as a body condition index, body mass divided by tarsus length) between experimental and control plots. We used point counts to examine Blackcap distribution, and standardized mist netting to collect demographic and biometric data. Incidence of singing Blackcaps was higher in nonbrowsed than in browsed plots, and singing males were recorded in nonbrowsed plots earlier in the season, indicating earlier and preferential territory establishment. Most Blackcaps, both males and females, were captured in vegetation prior to canopy closure (2–4 years of regrowth). Body condition was superior for male Blackcaps captured in nonbrowsed plots; for second-year males this was most marked in vegetation prior to canopy closure. We conclude that deer browsing in young woodland can alter habitat quality for understory-dependent species, with potential consequences for individual fitness and population productivity beyond the more obvious effects on population density

Solutions of the Faddeev-Yakubovsky equations for the four nucleons scattering states

The Faddeev-Yakubowsky equations in configuration space have been solved for the four nucleon system. The results with an S-wave interaction model in the isospin approximation are presented. They concern the bound and scattering states below the first three-body threshold. The elastic phase-shifts for the N+NNN reaction in different ($S,T$) channels are given and the corresponding low energy expansions are discussed. Particular attention is payed to the n+t elastic cross section. Its resonant structure is well described in terms of a simple NN interaction. First results concerning the S-matrix for the coupled N+NNN-NN+NN channels and the strong deuteron-deuteron scattering length are obtained.Comment: latex.tar.gz, 36 pages, 10 figures, 11 tables. To be published in Physical Review

Exploring events and distributed representations of text in multi-document summarization

In this article, we explore an event detection framework to improve multi-document summarization. Our approach is based on a two-stage single-document method that extracts a collection of key phrases, which are then used in a centrality-as-relevance passage retrieval model. We explore how to adapt this single-document method for multi-document summarization methods that are able to use event information. The event detection method is based on Fuzzy Fingerprint, which is a supervised method trained on documents with annotated event tags. To cope with the possible usage of different terms to describe the same event, we explore distributed representations of text in the form of word embeddings, which contributed to improve the summarization results. The proposed summarization methods are based on the hierarchical combination of single-document summaries. The automatic evaluation and human study performed show that these methods improve upon current state-of-the-art multi-document summarization systems on two mainstream evaluation datasets, DUC 2007 and TAC 2009. We show a relative improvement in ROUGE-1 scores of 16% for TAC 2009 and of 17% for DUC 2007.info:eu-repo/semantics/submittedVersio

The Nuclear Yukawa Model on a Lattice

We present the results of the quantum field theory approach to nuclear Yukawa model obtained by standard lattice techniques. We have considered the simplest case of two identical fermions interacting via a scalar meson exchange. Calculations have been performed using Wilson fermions in the quenched approximation. We found the existence of a critical coupling constant above which the model cannot be numerically solved. The range of the accessible coupling constants is below the threshold value for producing two-body bound states. Two-body scattering lengths have been obtained and compared to the non relativistic results.Comment: 15 page