Proton recoil polarization in exclusive (e,e'pp) reactions

The general formalism of nucleon recoil polarization in the (${\vec e},e'{\vec N}N$) reaction is given. Numerical predictions are presented for the components of the outgoing proton polarization and of the polarization transfer coefficient in the specific case of the exclusive $^{16}$O(${\vec e},e'{\vec p}p$)$^{14}$C knockout reaction leading to discrete states in the residual nucleus. Reaction calculations are performed in a direct knockout framework where final-state interactions and one-body and two-body currents are included. The two-nucleon overlap integrals are obtained from a calculation of the two-proton spectral function of $^{16}$O where long-range and short-range correlations are consistently included. The comparison of results obtained in different kinematics confirms that resolution of different final states in the $^{16}$O(${\vec e},e'{\vec p}p$)$^{14}$C reaction may act as a filter to disentangle and separately investigate the reaction processes due to short-range correlations and two-body currents and indicates that measurements of the components of the outgoing proton polarization may offer good opportunities to study short-range correlations.Comment: 12 pages, 6 figure

Short-range and tensor correlations in the 16^{16}O(e,e′'pn) reaction

The cross sections for electron induced two-nucleon knockout reactions are evaluated for the example of the $^{16}$O(e,e$'$pn)$^{14}$N reaction leading to discrete states in the residual nucleus $^{14}$N. These calculations account for the effects of nucleon-nucleon correlations and include the contributions of two-body meson exchange currents as the pion seagull, pion in flight and the isobar current contribution. The effects of short-range as well as tensor correlations are calculated within the framework of the coupled cluster method employing the Argonne V14 potential as a model for a realistic nucleon-nucleon interaction. The relative importance of correlation effects as compared to the contribution of the meson exchange currents depends on the final state of the residual nucleus. The cross section leading to specific states, like e.g. the ground state of $^{14}$N, is rather sensitive to the details of the correlated wave function.Comment: 16 pages, 9 figures include

Knockout of proton-neutron pairs from 16^{16}O with electromagnetic probes

After recent improvements to the Pavia model of two-nucleon knockout from $^{16}$O with electromagnetic probes the calculated cross sections are compared to experimental data from such reactions. Comparison with data from a measurement of the $^{16}$O(e,e$'$pn) reaction show much better agreement between experiment and theory than was previously observed. In a comparison with recent data from a measurement of the $^{16}$O($\gamma$,pn) reaction the model over-predicts the measured cross section at low missing momentum.Comment: 6 pages, 5 figure

Quenched Hadron Spectrum and Decay Constants on the lattice

In this talk we present the results obtained from a study of ${\cal O}(2000)$ (quenched) lattice configurations from the APE collaboration, at $6.0\le\beta\le 6.4$, using both the Wilson and the SW-Clover fermion action. We determine the light hadronic spectrum and the meson decay constants. For the light-light systems we find an agreement with the experimental data of $\sim 5$ for mesonic masses and $\sim 10$ for baryonic masses and pseudoscalar decay constants; a larger deviation is present for the vector decay constants. For the heavy-light decay constants we find $f_{D_s}=237 \pm 16 MeV, f_{D} = 221 \pm 17 MeV (f_{D_s}/f_D=1.07(4)), f_{B_s} = 205 \pm 35 MeV, f_{B} = 180 \pm 32 MeV (f_{B_s}/f_B=1.14(8))$, in good agreement with previous estimates.Comment: 8 pages, latex, Talk given at XXV ITEP Winter School of Physics, Moscow - Russia, 18-27 Feb 199

Final State Interaction in Exclusive (e,e′NN)(e,e'NN) Reactions

Contributions of nucleon-nucleon (NN) correlations, meson exchange currents and the residual final state interactions (FSI) on exclusive two-nucleon knock-out reactions induced by electron scattering are investigated. All contributions are derived from the same realistic meson exchange model for the NN interaction. Effects of correlations and FSI are determined in a consistent way by solving the NN scattering equation, the Bethe-Goldstone equation, for two nucleons in nuclear matter. One finds that the FSI re-scattering terms are non-negligible even if the two nucleons are emitted back to back.Comment: 8 pages, 5 figure

Deflazacort treatment of cystoid macular edema in patients affected by Retinitis Pigmentosa: a pilot study

Background. To investigate the efficacy of a long-term treatment with Deflazacort (DFZ), a third generation synthetic glucocorticoid, in patients affected by Retinitis Pigmentosa (RP) complicated by Cystoid Macular Edema (CME). Methods. A randomized group of 10 RP subjects were selected for this pilot study and treated with DFZ for one year according to a standard protocol. Far and near Best Corrected Visual Acuity (BCVA), fluorescein angiography (Heidelberg Retina Angiograph) and computerized perimetry (Humphrey Visual Field Analyzer) were statistically assessed. Results. Near visual acuities, fluorescein angiographic findings and perimetric data improved significantly (p < 0.01) while far BCVA varied only slightly (p < 0.05). No ocular or systemic side effects were recorded. Conclusions. Further case-control studies, also involving a larger number of patients, are required to confirm these preliminary results. However, the present investigation seem to suggest that DFZ could be effective in reducing fluorescein angiographic findings and improving perimetric data and near visual acuities in RP patients, even though the pathogenesis of CME remains poorly understood

Clinical pathogenesis of macular holes in patients affected by retinitis pigmentosa

Background. To define the main clinical mechanisms involved in the pathogenesis of macular holes (MH) in patients affected by Retinitis Pigmentosa (RP). Methods. 236 RP subjects were enrolled in this study and ophthalmologically examined according to a standard FIARP (Italian Federation of the RP Associations) protocol. The prevalence of posterior vitreous detachment (PVD) as well as all types of RP-related macular abnormalities - especially vitreoretinal interface alterations (VRIA), cystoid macular edema (CME), "bull's eye maculopathy" (BEM) and MH - was reported; statistical analyses and correlations were assessed by means of Student t test and Pearson X2. Results. VRIA and CME were observed in 26.15% and 9.45% of the cases respectively and resulted significantly associated with MH, since they were constantly present in 22 of the 25 eyes affected by MH (88%) (X2 = 50.4; p < 0.01). In particular, in 9 of these cases (40.9%) MH was correlated to both CME and VRIA, while in 11 (50%) and 2 (9.1%) eyes CME or, VRIA were present separately. A normal biomicroscopic macular appearance, PVD and BEM were found in 26.81%, 6.6% and 21.54% of the cases respectively. Conclusions. Further studies involving a larger number of patients are required to complete these preliminary results. However, the present investigation seem to confirm the data already reported in the literature, i.e. that pathogenesis of MH in RP is strictly correlated to the presence of VRIA, cellophane maculopathy and cystic foveal degeneration with CME

Two-proton overlap functions in the Jastrow correlation method and cross section of the 16^{16}O(e,e′pp)14(e,e^{\prime}pp)^{14}Cg.s._{\rm g.s.} reaction

Using the relationship between the two-particle overlap functions (TOF's) and the two-body density matrix (TDM), the TOF's for the $^{16}$O$(e,e^{\prime}pp)^{14}$C$_{\rm g.s.}$ reaction are calculated on the basis of a TDM obtained within the Jastrow correlation method. The main contributions of the removal of $^1S_0$ and $^3P_1$ $pp$ pairs from $^{16}$O are considered in the calculation of the cross section of the $^{16}$O$(e,e^{\prime}pp)^{14}$C$_{\rm g.s.}$ reaction using the Jastrow TOF's which include short-range correlations (SRC). The results are compared with the cross sections calculated with different theoretical treatments of the TOF's.Comment: 10 pages, 8 figures, ReVTeX

Optimization of Generalized Multichannel Quantum Defect reference functions for Feshbach resonance characterization

This work stresses the importance of the choice of the set of reference functions in the Generalized Multichannel Quantum Defect Theory to analyze the location and the width of Feshbach resonance occurring in collisional cross-sections. This is illustrated on the photoassociation of cold rubidium atom pairs, which is also modeled using the Mapped Fourier Grid Hamiltonian method combined with an optical potential. The specificity of the present example lies in a high density of quasi-bound states (closed channel) interacting with a dissociation continuum (open channel). We demonstrate that the optimization of the reference functions leads to quantum defects with a weak energy dependence across the relevant energy threshold. The main result of our paper is that the agreement between the both theoretical approaches is achieved only if optimized reference functions are used.Comment: submitte to Journal of Physics

Probing the chiral weak Hamiltonian at finite volumes

Non-leptonic kaon decays are often described through an effective chiral weak Hamiltonian, whose couplings ("low-energy constants") encode all non-perturbative QCD physics. It has recently been suggested that these low-energy constants could be determined at finite volumes by matching the non-perturbatively measured three-point correlation functions between the weak Hamiltonian and two left-handed flavour currents, to analytic predictions following from chiral perturbation theory. Here we complete the analytic side in two respects: by inspecting how small ("epsilon-regime") and intermediate or large ("p-regime") quark masses connect to each other, and by including in the discussion the two leading Delta I = 1/2 operators. We show that the epsilon-regime offers a straightforward strategy for disentangling the coefficients of the Delta I = 1/2 operators, and that in the p-regime finite-volume effects are significant in these observables once the pseudoscalar mass M and the box length L are in the regime ML \lsim 5.0.Comment: 37 pages. v2: some additions and clarifications; published versio