Unitary chiral dynamics in J/ΨJ/\Psi decays into VPPVPP and the role of the scalar mesons

We make a theoretical study of the \J decays into $\omega\pi\pi$, $\phi\pi\pi$, $\omega K \bar{K}$ and $\phi K\bar{K}$ using the techniques of the chiral unitary approach stressing the important role of the scalar resonances dynamically generated through the final state interaction of the two pseudoscalar mesons. We also discuss the importance of new mechanisms with intermediate exchange of vector and axial-vector mesons and the role played by the OZI rule in the \J\phi\pi\pi vertex, quantifying its effects. The results nicely reproduce the experimental data for the invariant mass distributions in all the channels considered.Comment: Prepared for the 10th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleo

How and when can one identify hadronic molecules in the baryon spectrum

A method to identify hadronic molecules in the particle spectrum is reviewed and the conditions for its applicability discussed. Special emphasis is put on the discussion of molecule candidates in the baryon spectrum.Comment: Talk presentent at NSTAR 2007, 5 - 8 September 2007, Bonn, German

Second--order equation of state with the Skyrme interaction. Cutoff and dimensional regularization with the inclusion of rearrangement terms

We evaluate the second--order (beyond--mean--field) contribution to the equation of state of nuclear matter with the effective Skyrme force and use cutoff and dimensional regularizations to treat the ultraviolet divergence produced by the zero--range character of this interaction. An adjustment of the force parameters is then performed in both cases to remove any double counting generated by the explicit computation of beyond--mean--field corrections with the Skyrme force. In addition, we include at second order the rearrangement terms associated to the density--dependent part of the Skyrme force and discuss their effect. Sets of parameters are proposed to define new effective forces which are specially designed for second--order calculations in nuclear matter.Comment: 29 figures, 9 table

Spin injection from EuS/Co multilayers into GaAs detected by polarized electroluminescence

We report on the successful spin injection from EuS/Co multilayers into (100) GaAs at low temperatures. The spin injection was verified by means of polarized electroluminescence (EL) emitted from AlGaAs/GaAs-based spin-light-emitting diodes in zero external magnetic field. Spin-polarized electrons were injected from prototype EuS/Co spin injector multilayers. The use of semiconducting and ferromagnetic EuS circumvents the impedance mismatch. The EL was measured in side emission with and without an external magnetic field. A circular polarization of 5% at 8 K and 0 T was observed. In view of the rather rough interface between the GaAs substrate and first EuS layer, improvement of the interface quality is expected to considerably enhance the injected electron spin polarization

Imperfect Imitation Can Enhance Cooperation

The promotion of cooperation on spatial lattices is an important issue in evolutionary game theory. This effect clearly depends on the update rule: it diminishes with stochastic imitative rules whereas it increases with unconditional imitation. To study the transition between both regimes, we propose a new evolutionary rule, which stochastically combines unconditional imitation with another imitative rule. We find that, surprinsingly, in many social dilemmas this rule yields higher cooperative levels than any of the two original ones. This nontrivial effect occurs because the basic rules induce a separation of timescales in the microscopic processes at cluster interfaces. The result is robust in the space of 2x2 symmetric games, on regular lattices and on scale-free networks.Comment: 4 pages, 4 figure

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

Relaxation and derelaxation of pure and hydrogenated amorphous silicon during thermal annealing experiments

The structural relaxation of pure amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) materials, that occurs during thermal annealing experiments, has been analysed by Raman spectroscopy and differential scanning calorimetry. Unlike a-Si, the heat evolved from a-Si:H cannot be explained by relaxation of the Si-Si network strain, but it reveals a derelaxation of the bond angle strain. Since the state of relaxation after annealing is very similar for pure and hydrogenated materials, our results give strong experimental support to the predicted configurational gap between a-Si and crystalline silicon.Comment: 15 pages, 3 figures, 1 table to be published in Applied Physics Letter