Dynamical generation of pseudoscalar resonances

We study the interactions between the f_0(980) and a_0(980) scalar resonances and the lightest pseudoscalar mesons. We first obtain the elementary interaction amplitudes, or interacting kernels, without including any ad hoc free parameter. This is achieved by using previous results on the nature of the lightest scalar resonances as dynamically generated from the rescattering of S-wave two-meson pairs. Afterwards, the interaction kernels are unitarized and the final S-wave amplitudes result. We find that these interactions are very rich and generate a large amount of pseudoscalar resonances that could be associated with the K(1460), \pi(1300), \pi(1800), \eta(1475) and X(1835). We also consider the exotic channels with isospin 3/2 and 1, having the latter positive G-parity. The former could be also resonant in agreement with a previous prediction.Comment: 31 pages, 9 figures, to be published in PR

Lesson Plan For Teaching Flannery O\u27Connor\u27s A Good Man Is Hard To Find

Suitable for high school and college and university classes. Developed by a Swarthmore College student, Adriana Obiols Roca, with feedback from Professor Peter Schmidt, as a final assignment in English 71D, The Short Story in the U.S., spring 2014. Learning Objectives. Students will: understand the differences between direct and indirect characterization and be able to identify examples of each; understand the uses of irony and foreshadowing in the story as well as more generally in literature; become acquainted with Flannery O’Connor and her writing style, particularly with her use of the grotesque; explore the complexity of the themes present in the story and the characters O’Connor has created, especially the Misfit and the grandmother; exercise a variety of critical thinking and analytical skills in order to form ideas and opinions about O\u27Connor\u27s story and her writing strategies; practice reading comprehension and summarization; employ and practice writing skills in an essay assignment

Nuclear symmetry energy and neutron skin thickness

The relation between the slope of the nuclear symmetry energy at saturation density and the neutron skin thickness is investigated. Constraints on the slope of the symmetry energy are deduced from the neutron skin data obtained in experiments with antiprotonic atoms. Two types of neutron skin are distinguished: the "surface" and the "bulk". A combination of both types forms neutron skin in most of nuclei. A prescription to calculate neutron skin thickness and the slope of symmetry energy parameter $L$ from the parity violating asymmetry measured in the PREX experiment is proposed.Comment: 12 pages, 5 figures, Presented at XXXII Mazurian Lakes Conference on Physics, Piaski, Poland, September 11-18, 201

Chiral Dynamics of scalar mesons: radiative ϕ\phi decay and σ\sigma in the medium through π0π0\pi^0 \pi^0 nuclear photoproduction

In order to assess the relevance of chiral dynamics in the scalar sector we address two recent problems: radiative decay of the $\phi$, for which there are quite recent data from Frascati, and the modification of the $\sigma$ properties in the nuclear medium seen through the $\pi^0 \pi^0$ photoproduction in nuclei.Comment: Talk given at the High Energy Physics Workshop "Scalar Mesons: an Interesting Puzzle for QCD", Utica, New York, May 200

Origin of the neutron skin thickness of 208Pb in nuclear mean-field models

We study whether the neutron skin thickness (NST) of 208Pb originates from the bulk or from the surface of the nucleon density distributions, according to the mean-field models of nuclear structure, and find that it depends on the stiffness of the nuclear symmetry energy. The bulk contribution to NST arises from an extended sharp radius of neutrons, whereas the surface contribution arises from different widths of the neutron and proton surfaces. Nuclear models where the symmetry energy is stiff, as typical relativistic models, predict a bulk contribution in NST of 208Pb about twice as large as the surface contribution. In contrast, models with a soft symmetry energy like common nonrelativistic models predict that NST of 208Pb is divided similarly into bulk and surface parts. Indeed, if the symmetry energy is supersoft, the surface contribution becomes dominant. We note that the linear correlation of NST of 208Pb with the density derivative of the nuclear symmetry energy arises from the bulk part of NST. We also note that most models predict a mixed-type (between halo and skin) neutron distribution for 208Pb. Although the halo-type limit is actually found in the models with a supersoft symmetry energy, the skin-type limit is not supported by any mean-field model. Finally, we compute parity-violating electron scattering in the conditions of the 208Pb parity radius experiment (PREX) and obtain a pocket formula for the parity-violating asymmetry in terms of the parameters that characterize the shape of the 208Pb nucleon densities.Comment: 11 pages, 4 figures; minor stylistic changes in text, new Ref. [56] added (new measurement of the neutron skin thickness of 208Pb

Density dependence of the symmetry energy from neutron skin thickness in finite nuclei

The density dependence of the symmetry energy around saturation density, characterized by the slope parameter L, is studied using information provided by the neutron skin thickness in finite nuclei. An estimate for L is obtained from experimental data on neutron skins extracted from antiprotonic atoms. We also discuss the ability of parity-violating elastic electron scattering to obtain information on the neutron skin thickness in 208Pb and to constrain the density dependence of the nuclear symmetry energy. The size and shape of the neutron density distribution of 208Pb predicted by mean-field models is briefly addressed. We conclude with a comparative overview of the L values predicted by several existing determinations.Comment: 17 pages, 10 figures, submitted to EPJA special volume on Nuclear Symmetry Energ

Low-lying dipole response: isospin character and collectivity in 68{}^{68}Ni, 132{}^{132}Sn and 208{}^{208}Pb

The isospin character, the collective or single-particle nature, and the sensitivity to the slope of the nuclear symmetry energy of the low-energy isovector dipole response (known as pygmy dipole resonance) are nowadays under debate. In the present work we study, within the fully self-consistent non-relativistic mean field (MF) approach based on Skyrme Hartree-Fock plus Random Phase Approximation (RPA), the measured even-even nuclei ${}^{68}$Ni, ${}^{132}$Sn and ${}^{208}$Pb. To analyze the model dependence in the predictions of the pygmy dipole strength, we employ three different Skyrme parameter sets. We find that both the isoscalar and the isovector dipole responses of all three nuclei show a low-energy peak that increases in magnitude, and is shifted to larger excitation energies, with increasing values of the slope of the symmetry energy at saturation. We highlight the fact that the collectivity associated with the RPA state(s) contributing to this peak is different in the isoscalar and isovector case, or in other words it depends on the external probe. While the response of these RPA states to an isovector operator does not show a clear collective nature, the response to an isoscalar operator is recognizably collective, for {\it all} analyzed nuclei and {\it all} studied interactions.Comment: Submitted to Phys. Rev.

Analysis of bulk and surface contributions in the neutron skin of nuclei

The neutron skin thickness of nuclei is a sensitive probe of the nuclear symmetry energy having multiple implications for nuclear and astrophysical studies. However, precision measurements of this observable are difficult. The analysis of the experimental data may imply some assumptions about the bulk or surface nature of the formation of the neutron skin. Here, we study the bulk or surface character of neutron skins of nuclei following from calculations with Gogny, Skyrme, and covariant nuclear mean-field interactions. These interactions are successful in describing nuclear charge radii and binding energies but predict different values for neutron skins. We perform the study by fitting two-parameter Fermi distributions to the calculated self-consistent neutron and proton densities. We note that the equivalent sharp radius is a more suitable reference quantity than the half-density radius parameter of the Fermi distributions to discern between the bulk and surface contributions in neutron skins. We present calculations for nuclei in the stability valley and for the isotopic chains of Sn and Pb.Comment: 13 pages, 9 figure

On the physical meaning of the 2.1 keV absorption feature in 4U 1538-52

The improvement of the capabilities of nowadays X-ray observatories, like Chandra or XMM-Newton, offers the possibility to detect both absorption and emission lines and to study the nature of the matter surrounding the neutron star in X-ray binaries and the phenomena that produce these lines. The aim of this work is to discuss the different physical scenarios in order to explain the meaning of the significant absorption feature present in the X-ray spectrum of 4U 1538-52. Using the last available calibrations, we discard the possibility that this feature is due to calibration, gain effects or be produced by the X-ray background or a dust region. Giving the energy resolution of the XMM-Newton telescope we could not establish if the line is formed in the atmosphere of the neutron star or by the dispersion of the stellar wind of the optical counterpart.Comment: 6 pages, 2 multipanel figures, accepted for publication on Proceedings of "An INTEGRAL view of the high-energy sky (the first 10 years)" the 9th INTEGRAL Workshop, October 15-19, 2012, Paris, France, in Proceedings of Science (INTEGRAL 2012), Eds. A. Goldwurm, F. Lebrun and C. Winkler, (http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176), id PoS(INTEGRAL 2012)03