Hard Break-Up of Two-Nucleons and QCD Dynamics of NN Interaction

We discus recent developments in theory of high energy two-body break-up of few-nucleon systems. The characteristics of these reactions are such that the hard two-body quasielastic subprocess can be clearly separated from the accompanying soft subprocesses. We discuss in details the hard rescattering model(HRM) in which hard photodisintegration develops in two stages. At first, photon knocks-out an energetic quark which rescatters subsequently with a quark of the other nucleon. The latter provides a mechanism of sharing the initial high momentum of the photon between two outgoing nucleons. This final state hard rescattering can be expressed through the hard NN scattering amplitude. Within HRM we discuss hard break-up reactions involving D and 3He targets and demonstrate how these reactions are sensitive to the dynamics of hard pn and pp interaction. Another development of HRM is the prediction of new helicity selection mechanism for hard two-body reactions, which was apparently confirmed in the recent JLab experiment.Comment: Invited talk at 6th International Conference on Perspective in Hadronic Physics, Trieste, Italy, 12-18 May 2008. Submitted to AIP Conf.Pro

Exploring the transverse spin structure of the nucleon

We discuss our present understanding of the transverse spin structure of the nucleon and of related properties originating from parton transverse motion. Starting from the transversity distribution and the ways to access it, we then address the role played by spin and transverse momentum dependent (TMD) distributions in azimuthal and transverse single spin asymmetries. The latest extractions of the Sivers, Collins and transversity functions are also presented.Comment: 8 pages, 6 ps figures, uses aipproc.cls. Invited talk at "6th International Conference on Perspectives in Hadronic Physics (Hadron 08)", Trieste, Italy, 12-18 May 2008. Submitted to AIP Conf.Pro

Electromagnetic Transition Form Factors of Nucleon Resonances

Recent measurements of nucleon resonance transition form factors with CLAS at Jefferson Lab are discussed. The new data resolve a long-standing puzzle of the nature of the Roper resonance, and confirm the assertion of the symmetric constituent quark model of the Roper as the first radial excitation of the nucleon. The data on $n\pi^+$ production at high $Q^2$ confirm the slow fall off of the $S_{11}(1535)$ transition form factor with $Q^2$, and better constrain the branching ratios $\beta_{N\pi}=0.50$ and $\beta_{N\eta}=0.45$. Also, new results on the transition amplitudes for the $D_{13}(1520)$ resonance are presented showing a rapid change from helicity 3/2 dominance seen at the real photon point to helicty 1/2 dominance at higher $Q^2$.Comment: 5 pages, 7 figure

Electromagnetic Form Factors of Hadrons in Quantum Field Theories

In this talk, recent results are presented of calculations of electromagnetic form factors of hadrons in the framework of two quantum field theories (QFT), (a) Dual-Large $N_c$ QCD (Dual-$QCD_\infty$) for the pion, proton, and $\Delta(1236)$, and (b) the Kroll-Lee-Zumino (KLZ) fully renormalizable Abelian QFT for the pion form factor. Both theories provide a QFT platform to improve on naive (tree-level) Vector Meson Dominance (VMD). Dual-$QCD_\infty$ provides a tree-level improvement by incorporating an infinite number of zero-width resonances, which can be subsequently shifted from the real axis to account for the time-like behaviour of the form factors. The renormalizable KLZ model provides a QFT improvement of VMD in the framework of perturbation theory. Due to the relative mildness of the $\rho\pi\pi$ coupling, and the size of loop suppression factors, the perturbative expansion is well defined in spite of this being a strong coupling theory. Both approaches lead to considerable improvements of VMD predictions for electromagnetic form factors, in excellent agreement with data.Comment: Invited talk at the Sixth International Conference on Perspectives in Hadronic Physics, ICTP, Trieste, Italy, May 200

Short-range nucleon correlations and neutrino emission by neutron stars

We argue that significant probability of protons with momenta above their Fermi surface leads for proton concentrations p/n > 1/8 to the enhancement of termally excited direct and modified URCA processes within a cold neutron star, and to a nonzero probability of direct URCA processes for small proton concentrations (p/n < 1/8). We evaluate high momentum tails of neutron, proton and electrons distributions within a neutron star. We expect also significantly faster neutrino cooling of hyperon stars.Comment: 7 pages, updated version to be published in Proceedings of Sixth International Conference on Perspectives in Hadronic Physics, Trieste, May 200

Studies of Parton Propagation and Hadron Formation in the Space-Time Domain

Over the past decade, new data from HERMES, Jefferson Lab, Fermilab, and RHIC that connect to parton propagation and hadron formation have become available. Semi-inclusive DIS on nuclei, the Drell-Yan reaction, and heavy-ion collisions all bring different kinds of information on parton propagation within a medium, while the most direct information on hadron formation comes from the DIS data. Over the next decade one can hope to begin to understand these data within a unified picture. We briefly survey the most relevant data and the common elements of the physics picture, then highlight the new Jefferson Lab data, and close with a prospective for the future.Comment: Invited talk delivered at the Sixth International Conference on Perspectives in Hadronic Physics, ICTP, Trieste, Italy, 12-16 May 2008. 8 pages, 5 figure

Relativistic Quark-Model Results for Baryon Ground and Resonant States

Latest results from a study of baryon ground and resonant states within relativistic constituent quark models are reported. After recalling some typical spectral properties, the description of ground states, especially with regard to the nucleon and hyperon electromagnetic structures, is addressed. In the following, recent covariant predictions for pion, eta, and kaon partial decay widths of light and strange baryon resonances below 2 GeV are summarized. These results exhibit a characteristic pattern that is distinct from nonrelativistic or relativized decay studies performed so far. Together with a detailed analysis of the spin, flavor, and spatial structures of the wave functions, it supports a new and extended classification scheme of baryon ground and resonant states into SU(3) flavor multiplets

Jet correlations from unintegrated parton distributions

Transverse-momentum dependent parton distributions can be introduced gauge-invariantly in QCD from high-energy factorization. We discuss Monte Carlo applications of these distributions to parton showers and jet physics, with a view to the implications for the Monte Carlo description of complex hadronic final states with multiple hard scales at the LHC.Comment: 8 pages, 4 figure

Future directions for probing two and three nucleon short-range correlations at high energies

We summarize recent progress in the studies of the short-rang correlations (SRC) in nuclei in high energy electron and hadron nucleus scattering and suggest directions for the future high energy studies aimed at establishing detailed structure of two-nucleon SRCs, revealing structure of three nucleon SRC correlations and discovering non-nucleonic degrees of freedom in nuclei.Comment: 8 pages, 1 figur