Deeply Virtual Compton Scattering on the Deuteron

We study deeply virtual Compton scattering (DVCS) on a deuteron target. We model the Generalized Quark Distributions in the deuteron by using the impulse approximation for the lowest Fock-space state. Numerical predictions are given for the unpolarized cross sections for the kinematical regimes relevant for JLab and HERMES at HERA. Differential cross sections show the same pattern as for the proton case and at low values of t they are of comparable size.Comment: 6 pages, 4 eps figures. Contribution to the European Workshop on the QCD Structure of the Nucleon (QCD-N'02), Ferrara, Italy, 3-6 Apr 200

Quark correlations and gluon propagators in elastic vector meson production

We study the behavior of the differential cross section for vector meson photoproduction at large momentum transfer in the two-gluon exchange model. We focus on the treatment of two-quark correlation function in the proton and on gluon propagators with a dynamically generated mass. We find that only the large t region is sensitive to the particular details of these inputs.Comment: 4 pages, 2 figures, espcrc1.sty included, Proceedings of the Third International Conference on Perspectives in Hadronic Physic

Real and Virtual Compton Scattering in a Regge Approach

We study Real and Deeply Virtual Compton Scattering in a model based on Regge trajectories and two-gluon exchange. In the kinematic regime of current experiments, the hadronic component of the outgoing real photon plays a major role. We analyze the spin structure of Compton scattering at large momentum transfer and give predictions for several spin asymmetries. In the DVCS channel, a fairly good agreement is obtained for the recently measured beam spin and charge asymmetries.Comment: 12 pages; 6 figures This revised version corrects a mumerical mistake in the evaluation of the conversion factor between vector mesons and Compton amplitudes. Also, more details are given on the parameters of the sigma meson amplitud

A consistent explanation of the Roper phenomenology

We study the electromagnetic transitions of the Roper N(1440) resonance. Our results, when combined with the previously obtained for the mass and the pionic strong decay widths of the Roper, show that within a non-relativistic constituent quark model scheme, a comprehensible understanding of the Roper phenomenology can be achieved. They also seem to support the view of the Roper as a radial excitation of the nucleon, though more experimental data are needed to reach a definitive conclusion.Comment: 14 pages, 4 figures (7 postscript files). Some referencess adde

Social influence analysis in microblogging platforms - a topic-sensitive based approach

The use of Social Media, particularly microblogging platforms such as Twitter, has proven to be an effective channel for promoting ideas to online audiences. In a world where information can bias public opinion it is essential to analyse the propagation and influence of information in large-scale networks. Recent research studying social media data to rank users by topical relevance have largely focused on the “retweet", “following" and “mention" relations. In this paper we propose the use of semantic profiles for deriving influential users based on the retweet subgraph of the Twitter graph. We introduce a variation of the PageRank algorithm for analysing users’ topical and entity influence based on the topical/entity relevance of a retweet relation. Experimental results show that our approach outperforms related algorithms including HITS, InDegree and Topic-Sensitive PageRank. We also introduce VisInfluence, a visualisation platform for presenting top influential users based on a topical query need

Strong Pionic Decays From a Spectroscopic Quark Model

From a refined non-relativistic quark model that fits the baryonic low-energy spectrum the study of strong pion decay processes within an elementary emission model scheme points out the need of incorporating size-contributing components into the baryon wave functions. In particular the effect of a (qqq qantiq) component is investigated in the framework of a quark pair creation model.Comment: 26 pages, 9 figures (1 postscript file), LaTe