The Color Dipole Picture of low-x DIS: Model-Independent and Model-Dependent Results

We present a detailed examination of the color-dipole picture (CDP) of low-$x$ deep inelastic scattering. We discriminate model-independent results, not depending on a specific parameterization of the dipole cross section, from model-dependent ones. The model-independent results include the ratio of the longitudinal to the transverse photoabsorption cross section at large $Q^2$, or equivalently the ratio of the longitudinal to the unpolarized proton structure function, $F_L (x,Q^2)=0.27 F_2 (x, Q^2)$, as well as the low-$x$ scaling behavior of the total photoabsorption cross section $\sigma_{\gamma^*p} (W^2, Q^2)=\sigma_{\gamma^*p} (\eta (W^2, Q^2))$ as $\log (1 / \eta (W^2, Q^2))$ for $\eta (W^2, Q^2) <1$, and as $1/\eta (W^2, Q^2)$ for $\eta (W^2, Q^2) \gg 1$. Here, $\eta (W^2, Q^2)$ denotes the low-$x$ scaling variable, $\eta (W^2, Q^2)=(Q^2 + m^2_0) / \Lambda^2_{sat} (W^2)$ with $\Lambda^2_{sat} (W^2)$ being the saturation scale. The model-independent analysis also implies $\lim\limits_{W^2\rightarrow\infty, Q^2 {\rm fixed}} \sigma_{\gamma^*p} (W^2, Q^2) / \sigma_{\gamma p} (W^2) \rightarrow 1$ at any $Q^2$ for asymptotically large energy, $W$. Consistency with pQCD evolution determines the underlying gluon distribution and the numerical value of $C_2 = 0.29$ in the expression for the saturation scale, $\Lambda^2 (W^2) \sim (W^2)^{C_2}$. In the model-dependent analysis, by restricting the mass of the actively contributing $q \bar q$ fluctuations by an energy-dependent upper bound, we extend the validity of the color-dipole picture to $x \cong Q^2 / W^2 \le 0.1$. The theoretical results agree with the world data on DIS for $0.036 {\rm GeV}^2 \le Q^2 \le 316 {\rm GeV}^2$.Comment: 77 pages, 30 figure

Multipole analysis of spin observables in vector meson photoproduction

A multipole analysis of vector meson photoproduction is formulated as a generalization of the pseudoscalar meson case. Expansion of spin observables in the multipole basis and behavior of these observables near threshold and resonances are examined.Comment: 15 pages, latex, 2 figure

Innovative observing strategy and orbit determination for Low Earth Orbit Space Debris

We present the results of a large scale simulation, reproducing the behavior of a data center for the build-up and maintenance of a complete catalog of space debris in the upper part of the low Earth orbits region (LEO). The purpose is to determine the performances of a network of advanced optical sensors, through the use of the newest orbit determination algorithms developed by the Department of Mathematics of Pisa (DM). Such a network has been proposed to ESA in the Space Situational Awareness (SSA) framework by Carlo Gavazzi Space SpA (CGS), Istituto Nazionale di Astrofisica (INAF), DM, and Istituto di Scienza e Tecnologie dell'Informazione (ISTI-CNR). The conclusion is that it is possible to use a network of optical sensors to build up a catalog containing more than 98% of the objects with perigee height between 1100 and 2000 km, which would be observable by a reference radar system selected as comparison. It is also possible to maintain such a catalog within the accuracy requirements motivated by collision avoidance, and to detect catastrophic fragmentation events. However, such results depend upon specific assumptions on the sensor and on the software technologies

Elastic electron deuteron scattering with consistent meson exchange and relativistic contributions of leading order

The influence of relativistic contributions to elastic electron deuteron scattering is studied systematically at low and intermediate momentum transfers ($Q^2\leq 30$ fm$^{-2}$). In a $(p/M)$-expansion, all leading order relativistic $\pi$-exchange contributions consistent with the Bonn OBEPQ models are included. In addition, static heavy meson exchange currents including boost terms and lowest order $\rho\pi\gamma$-currents are considered. Sizeable effects from the various relativistic two-body contributions, mainly from $\pi$-exchange, have been found in form factors, structure functions and the tensor polarization $T_{20}$. Furthermore, static properties, viz. magnetic dipole and charge quadrupole moments and the mean square charge radius are evaluated.Comment: 15 pages Latex including 5 figures, final version accepted for publication in Phys.Rev.C Details of changes: (i) The notation of the curves in Figs. 1 and 2 have been clarified with respect to left and right panels. (ii) In Figs. 3 and 4 an experimental point for T_20 has been added and a corresponding reference [48] (iii) At the end of the text we have added a paragraph concerning the quality of the Bonn OBEPQ potential

Color coherent phenomena on nuclei and the QCD evolution equation

We review the phenomenon of color coherence in quantum chromodynamics (QCD), its implications for hard and soft processes with nuclei, and its experimental manifestations. The relation of factorization theorems in QCD with color coherence phenomena in deep inelastic scattering (DIS) and color coherence phenomena in hard exclusive processes is emphasized. Analyzing numerically the QCD evolution equation for conventional and skewed parton densities in nuclei, we study the onset of generalized color transparency and nuclear shadowing of the sea quark and gluon distributions in nuclei as well as related phenomena. Such novel results as the dependence of the effective coherence length on $Q^2$ and general trends of the QCD evolution are discussed. The limits of the applicability of the QCD evolution equation at small Bjorken $x$ are estimated by comparing the inelastic quark-antiquark- and two gluon-nucleon (nucleus) cross sections, calculated within the DGLAP approximation, with the dynamical boundaries, which follow from the unitarity of the $S$ matrix for purely QCD interactions. We also demonstrate that principles of color coherence play an important role in the processes of soft diffraction off nuclei.Comment: 58 pages, 19 figures, Revtex. Minor editor's changes, final version published in J.Phys. G27 (2001) R23-6

New fermions and a vector-like third generation in SU(3)c⊗SU(3)L⊗U(1)NSU(3)_c\otimes SU(3)_L\otimes U(1)_N models

We study two 3-3-1 models with i) five (four) charge 2/3 ($-1/3$) quarks and, ii) four (five) charge 2/3 ($-1/3$) quarks and a vector-like third generation. Possibilities beyond these models are also briefly considered.Comment: 32 pages, Revtex 3.0, no figure

J/Psi Photoproduction in a Dual Model

J/Psi photoproduction is studied in the framework of the analytic S-matrix theory. The differential and integrated elastic cross sections for J/Psi photoproduction are calculated from a Dual Amplitude with Mandelstam Analyticity. It is argued that at low energies, the background, which is the low-energy equivalent of the high-energy diffraction replaces the Pomeron exchange. The onset of the high energy Pomeron dominance is estimated from the fits to the data.Comment: 10 pages, 7 figures. Dedicated to Professor Anatoly I. Bugrij on the occasion of his 60-th birthda

Radiative corrections to polarization observables in elastic electron-deuteron scattering in leptonic variables

The model--independent QED radiative corrections to polarization observables in elastic scattering of unpolarized and longitudinally--polarized electron beam by the deuteron target have been calculated in leptonic variables. The experimental setup when the deuteron target is arbitrarily polarized is considered and the procedure for applying derived results to the vector or tensor polarization of the recoil deuteron is discussed. The basis of the calculations consists of the account for all essential Feynman diagrams which results in the form of the Drell-Yan representation for the cross-section and use of the covariant parametrization of the deuteron polarization state. The numerical estimates of the radiative corrections are given for the case when event selection allows the undetected particles (photons and electron-positron pairs) and the restriction on the lost invariant mass is used.Comment: 43 pages,3 figures. To be published in ZhTEF. revised 14.02.2012. arXiv admin note: text overlap with arXiv:nucl-ex/0002003 by other author

Oxidative and nitrative alpha-synuclein modifications and proteostatic stress: implications for disease mechanisms and interventions in synucleinopathies

Alpha-synuclein (ASYN) is a major constituent of the typical protein aggregates observed in several neurodegenerative diseases that are collectively referred to as synucleinopathies. A causal involvement of ASYN in the initiation and progression of neurological diseases is suggested by observations indicating that single-point (e.g., A30P, A53T) or multiplication mutations of the gene encoding for ASYN cause early onset forms of Parkinson's disease (PD). The relative regional specificity of ASYN pathology is still a riddle that cannot be simply explained by its expression pattern. Also, transgenic over-expression of ASYN in mice does not recapitulate the typical dopaminergic neuronal death observed in PD. Thus, additional factors must contribute to ASYN-related toxicity. For instance, synucleinopathies are usually associated with inflammation and elevated levels of oxidative stress in affected brain areas. In turn, these conditions favor oxidative modifications of ASYN. Among these modifications, nitration of tyrosine residues, formation of covalent ASYN dimers, as well as methionine sulfoxidations are prominent examples that are observed in post-mortem PD brain sections. Oxidative modifications can affect ASYN aggregation, as well as its binding to biological membranes. This would affect neurotransmitter recycling, mitochondrial function and dynamics (fission/fusion), ASYN's degradation within a cell and, possibly, the transfer of modified ASYN to adjacent cells. Here, we propose a model on how covalent modifications of ASYN link energy stress, altered proteostasis, and oxidative stress, three major pathogenic processes involved in PD progression. Moreover, we hypothesize that ASYN may act physiologically as a catalytically regenerated scavenger of oxidants in healthy cells, thus performing an important protective role prior to the onset of disease or during aging