The two pion decay of the Roper resonance

We evaluate the two pion decay of the Roper resonance in a model where explicit re-scattering of the two final pions is accounted for by the use of unitarized chiral perturbation theory. Our model does not include an explicit $\epsilon$ or $\sigma$ scalar-isoscalar meson decay mode, instead it generates it dynamically by means of the pion re-scattering. The two ways, explicit or dynamically generated, of introducing this decay channel have very different amplitudes. Nevertheless, through interference with the other terms of the model we are able to reproduce the same phenomenology as models with explicit consideration of the $\epsilon$ meson.Comment: 17 latex pages, 11 eps figures. A few misprints corrected. A few new references. Version accepted for publication in Phys. Rev.

Eta meson production in nucleon-nucleon collisions within an effective Lagrangian model

We investigate the pp --> pp eta and pn --> pn eta reactions within an effective Lagrangian model for laboratory kinetic energies ranging from very close to eta meson production threshold to about 10 GeV. Production amplitudes include contributions from the mechanism of excitation, propagation and decay of N*(1535), N*(1650), and N*(1710) baryonic resonances. The initial interaction between two incoming nucleons is modeled by the exchange of pi, rho, omega and sigma mesons where the vertex parameters are taken to be the same as those used in the previous applications of this model. Parameters of the resonance vertices also have been taken from our earlier studies wherever applicable. Calculations have been done for total as well as differential eta production cross sections. To describe the data for energies closer to the production threshold final state interactions among the out-going particles have been included by means of a generalized Watson-Migdal method. Terms corresponding to the excitation of N*(1535) resonance and pion exchange process dominate the cross sections. With a single set of vertex parameters our model is able to describe the available data well on total cross sections for beam energies ranging from close to threshold to upto 10 GeV.Comment: 33 pages, 11 figures, one new appendix added, discussions extende

Contribution of the massive photon decay channel to neutrino cooling of neutron stars

We consider massive photon decay reactions via intermediate states of electron-electron-holes and proton-proton-holes into neutrino-antineutrino pairs in the course of neutron star cooling. These reactions may become operative in hot neutron stars in the region of proton pairing where the photon due to the Higgs-Meissner effect acquires an effective mass $m_{\gamma}$ that is small compared to the corresponding plasma frequency. The contribution of these reactions to neutrino emissivity is calculated; it varies with the temperature and the photon mass as $T^{3/2}m_{\gamma}^{7/2} e^{-m_{\gamma}/T}$ for $T < m_{\gamma}$. Estimates show that these processes appear as extra efficient cooling channels of neutron stars at temperatures $T \simeq (10^9-10^{10})$ K.Comment: accepted to publication in Zh. Eksp. Teor. Fiz. (JETP

The decay ρ0→π++π−+γ\rho^{0}\to \pi^{+}+\pi^{-}+\gamma and the coupling constant gρσγ_{\rho\sigma\gamma}

The experimental branching ratio for the radiative decay $\rho^{0}\to\pi^{+}+\pi^{-}+\gamma$ is used to estimate the coupling constant $g_{\rho\sigma\gamma}$ for a set of values of $\sigma$-meson parameters M$_{\sigma}$ and $\Gamma_{\sigma}$. Our results are quite different than the values of this constant used in the literature.Comment: 9 pages(RevTex), 5 ps figure

Neutrino Pair Bremsstrahlung in Neutron Star Crusts: a Reappraisal

We demonstrate that band-structure effects suppress bremsstrahlung of neutrino pairs by electrons in the crusts of neutron stars at temperatures of the order of $5\times 10^9 \,{\rm K}$ and below. Taking this into account, together with the fact that recent work indicates that the masses of neutron star crusts are considerably smaller than previously estimated, we find neutrino pair bremsstrahlung to be much less important for the thermal evolution of neutron stars than earlier calculations suggested.Comment: 11 plain LaTeX pages, 3 figures available on request, NORDITA-93/72 A/S/

Photoproduction of scalar mesons on protons and nuclei

We study the photoproduction of scalar mesons close to the threshold of f_0(980) and a_0(980) using a unitary chiral model. Peaks for both resonances show up in the invariant mass distributions of pairs of pseudoscalar mesons. A discussion is made on the photoproduction of these resonances in nuclei, which can shed light on their nature, a subject of continuous debate.Comment: 25 pages, 9 figures, accepted for publication in Phys Rev

Modified Quark-Meson Coupling Model for Nuclear Matter

The quark-meson coupling model for nuclear matter, which describes nuclear matter as non-overlapping MIT bags bound by the self-consistent exchange of scalar and vector mesons, is modified by introducing medium modification of the bag constant. We model the density dependence of the bag constant in two different ways: one invokes a direct coupling of the bag constant to the scalar meson field, and the other relates the bag constant to the in-medium nucleon mass. Both models feature a decreasing bag constant with increasing density. We find that when the bag constant is significantly reduced in nuclear medium with respect to its free-space value, large canceling isoscalar Lorentz scalar and vector potentials for the nucleon in nuclear matter emerge naturally. Such potentials are comparable to those suggested by relativistic nuclear phenomenology and finite-density QCD sum rules. This suggests that the reduction of bag constant in nuclear medium may play an important role in low- and medium-energy nuclear physics.Comment: Part of the text is reordered, revised version to appear in Phys. Rev. C. 19 pages, ReVTeX, 4 figures embedde

An international collaborative evaluation of central serous chorioretinopathy: different therapeutic approaches and review of literature. The European Vitreoretinal Society central serous chorioretinopathy study

Purpose: To study and compare the efficacy of different therapeutic options for the treatment of central serous chorioretinopathy (CSCR). Methods: This is a nonrandomized, international multicentre study on 1719 patients (1861 eyes) diagnosed with CSCR, from 63 centres (24 countries). Reported data included different methods of treatment and both results of diagnostic examinations [fluorescein angiography and/or optical coherent tomography (OCT)] and best-corrected visual acuity (BCVA) before and after therapy. The duration of observation had a mean of 11&nbsp;months but was extended in a minority of cases up to 7&nbsp;years. The aim of this study is to evaluate the efficacy of the different therapeutic options of CSCR in terms of both visual (BCVA) and anatomic (OCT) improvement. Results: One thousand seven hundred nineteen patients (1861 eyes) diagnosed with CSCR were included. Treatments performed were nonsteroidal anti-inflammatory eye drops, laser photocoagulation, micropulse diode laser photocoagulation, photodynamic therapy (PDT; Standard PDT, Reduced-dose PDT, Reduced-fluence PDT), intravitreal (IVT) antivascular endothelial growth factor injection (VEGF), observation and other treatments. The list of the OTHERS included both combinations of the main proposed treatments or a variety of other treatments such as eplerenone, spironolactone, acetazolamide, beta-blockers, anti-anxiety drugs, aspirin, folic acid, methotrexate, statins, vitis vinifera extract medication and pars plana vitrectomy. The majority of the patients were men with a prevalence of 77%. The odds ratio (OR) showed a partial or complete resolution of fluid on OCT with any treatment as compared with observation. In univariate analysis, the anatomical result (improvement in subretinal fluid using OCT at 1&nbsp;month) was favoured by age &lt;60&nbsp;years (p&nbsp;&lt;&nbsp;0.005), no previous observation (p&nbsp;&lt;&nbsp;0.0002), duration less than 3&nbsp;months (p&nbsp;&lt;&nbsp;0.0001), absence of CSCR in the fellow eye (p&nbsp;=&nbsp;0.04), leakage outside of the arcade (p&nbsp;=&nbsp;0.05) and fluid height &gt;500&nbsp;\u3bcm (p&nbsp;=&nbsp;0.03). The OR for obtaining partial or complete resolution showed that anti-VEGF and eyedrops were not statistically significant; whereas PDT (8.5), thermal laser (11.3) and micropulse laser (8.9) lead to better anatomical results with less variability. In univariate analysis, the functional result at 1&nbsp;month was favoured by first episode (p&nbsp;=&nbsp;0.04), height of subretinal fluid &gt;500&nbsp;\u3bcm (p&nbsp;&lt;&nbsp;0.0001) and short duration of observation (p&nbsp;=&nbsp;0.02). Finally, there was no statistically significant difference among the treatments at 12&nbsp;months. Conclusion: Spontaneous resolution has been described in a high percentage of patients. Laser (micropulse and thermal) and PDT seem to lead to significant early anatomical improvement; however, there is little change beyond the first month of treatment. The real visual benefit needs further clarification