Extraction of the Compton Form Factor H from DVCS measurements at Jefferson Lab

In the framework of Generalised Parton Distributions, we study the helicity-dependent and independent cross sections measured in Hall A and the beam spin asymmetries measured in Hall B at Jefferson Laboratory. We perform a global fit of these data and fits on each kinematical bin. We extract the real and imaginary parts of the Compton Form Factor $\mathcal{H}$ under the main hypothesis of dominance of the Generalised Parton Distribution $H$ and twist 2 accuracy. We discuss our results and compare to previous extractions as well as to the VGG model. We pay extra attention to the estimation of errors on the extraction of $\mathcal{H}$.Comment: 24 pages, 8 figure

Chiral-odd generalized parton distributions, transversity decomposition of angular momentum, and tensor charges of the nucleon

The forward limit of the chiral-odd generalized parton distributions (GPDs) and their lower moments are investigated within the framework of the chiral quark soliton model (CQSM), with particular emphasis upon the transversity decomposition of nucleon angular momentum proposed by Burkardt. A strong correlation between quark spin and orbital angular momentum inside the nucleon is manifest itself in the derived second moment sum rule within the CQSM, thereby providing with an additional support to the qualitative connection between chiral-odd GPDs and the Boer-Mulders effects. We further confirm isoscalar dominance of the corresponding first moment sum rule, which indicates that the Boer-Mulders functions for the $u$- and $d$-quarks have roughly equal magnitude with the same sign. Also made are some comments on the recent empirical extraction of the tensor charges of the nucleon by Anselmino et al. We demonstrate that a comparison of their result with any theoretical predictions must be done with great care, in consideration of fairly strong scale dependence of tensor charges, especially at lower renormalization scale.Comment: version to appear in Phys. Rev.

Extended Ordered Paired Comparison Models with Application to Football Data from German Bundesliga

A general paired comparison model for the evaluation of sports competitions is proposed. It efficiently uses the available information by allowing for ordered response categories and team-specific home advantage effects. Penalized estimation techniques are used to identify clusters of teams that share the same ability. The model is extended to include team-specific explanatory variables. It is shown that regularization techniques allow to identify the contribution of explanatory variables to the success of teams. The usefulness of the methods is demonstrated by investigating the performance and its dependence on the budget for football teams of the German Bundesliga

Invasion controlled pattern formation in a generalized multi-species predator-prey system

Rock-scissors-paper game, as the simplest model of intransitive relation between competing agents, is a frequently quoted model to explain the stable diversity of competitors in the race of surviving. When increasing the number of competitors we may face a novel situation because beside the mentioned unidirectional predator-prey-like dominance a balanced or peer relation can emerge between some competitors. By utilizing this possibility in the present work we generalize a four-state predator-prey type model where we establish two groups of species labeled by even and odd numbers. In particular, we introduce different invasion probabilities between and within these groups, which results in a tunable intensity of bidirectional invasion among peer species. Our study reveals an exceptional richness of pattern formations where five quantitatively different phases are observed by varying solely the strength of the mentioned inner invasion. The related transition points can be identified with the help of appropriate order parameters based on the spatial autocorrelation decay, on the fraction of empty sites, and on the variance of the species density. Furthermore, the application of diverse, alliance-specific inner invasion rates for different groups may result in the extinction of the pair of species where this inner invasion is moderate. These observations highlight that beyond the well-known and intensively studied cyclic dominance there is an additional source of complexity of pattern formation that has not been explored earlier.Comment: 8 pages, 8 figures. To appear in PR

Beyond the black disk limit: from shadow to antishadow scattering mode

New mode in the hadron scattering is predicted to appear at the energies beyond $\sqrt{s}\simeq 2$ TeV: the antishadow scattering mode and the experiments at LHC and VLHC in hadronic reactions will be able to reveal it. The appearance of the antishadow scattering mode at these energies is considered on the basis of unitarity and geometrical notions of hadron interactions. Connections with the nonperturbative--QCD models are discussed.Comment: 25 pages, 2 figure

Extraction of the Compton Form Factor H from DVCS Measurements in the Quark Sector

Working at twist 2 accuracy and assuming the dominance of the Generalized Parton Distribution H we study the helicity-dependent and independent cross sections measured in Hall A, the beam spin asymmetries measured in Hall B at Jefferson Laboratory and beam charge, beam spin and target spin asymmetries measured by Hermes. We extract the real and imaginary parts of the Compton Form Factor H, the latter being obtained with a 20--50% uncertainty. We pay extra attention to the estimation of systematic errors on the extraction of H. We discuss our results and compare to other extractions as well as to the popular VGG model.Comment: 6 pages, 3 figures, Plenary talk given at the 12th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2010), Williamsburg, Virginia, USA, 31 May - 4 Jun 201

Scattering of vector mesons off nucleons

We construct a relativistic and unitary approach to 'high' energy pion- and photon-nucleon reactions taking the $\pi N, \pi \Delta$, $\rho N$, $\omega N$, $\eta N, K \Lambda, K \Sigma$ final states into account. Our scheme dynamically generates the s- and d-wave nucleon resonances N(1535), N(1650) and N(1520) and isobar resonances $\Delta(1620)$ and $\Delta(1700)$ in terms of quasi-local interaction vertices. The description of photon-induced processes is based on a generalized vector-meson dominance assumption which directly relates the electromagnetic quasi-local 4-point interaction vertices to the corresponding vertices involving the $\rho$ and $\omega$ fields. We obtain a satisfactory description of the elastic and inelastic pion- and photon-nucleon scattering data in the channels considered. The resulting s-wave $\rho$- and $\omega$-nucleon scattering amplitudes are presented. Using these amplitudes we compute the leading density modification of the $\rho$ and $\omega$ energy distributions in nuclear matter. We find a repulsive energy shift for the $\omega$ meson at small nuclear density but predict considerable strength in resonance-hole like $\omega$-meson modes. Compared to previous calculations our result for the $\rho$-meson spectral function shows a significantly smaller in-medium effect. This reflects a fairly small coupling strength of the N(1520) resonance to the $\rho N$ channel.Comment: 78 pages, 19 figures, moderately revised version, accepted in Nucl. Phys.