Hyperon effects on the properties of β\beta-stable neutron star matter

We present results from Brueckner-Hartree-Fock calculations for $\beta$-stable neutron star matter with nucleonic and hyperonic degrees of freedom employing the most recent parametrizations of the baryon-baryon interaction of the Nijmegen group. Only $\Sigma^-$ and $\Lambda$ are present up to densities $\sim 7\rho_0$. The corresponding equations of state are then used to compute properties of neutron stars such as masses and radii.Comment: 4 pages, contributed talk at HYP2000, Torino, 23-27 Oct. 200

Modern nucleon-nucleon potentials and symmetry energy in infinite matter

We study the symmetry energy in infinite nuclear matter employing a non-relativistic Brueckner-Hartree-Fock approach and using various new nucleon-nucleon (NN) potentials, which fit np and pp scattering data very accurately. The potential models we employ are the recent versions of the Nijmegen group, Nijm-I, Nijm-II and Reid93, the Argonne $V_{18}$ potential and the CD-Bonn potential. All these potentials yield a symmetry energy which increases with density, resolving a discrepancy that existed for older NN potentials. The origin of remaining differences is discussed.Comment: 17 pages, 10 figures included, elsevier latex style epsart.st

Isospin symmetry breaking nucleon-nucleon potentials and nuclear structure

Modern nucleon-nucleon (NN) potentials, which accurately fit the nucleon-nucleon scattering phase shifts, contain terms which break isospin symmetry. The effects of these symmetry violating terms on the bulk properties of nuclear matter are investigated. The predictions of the charge symmetry breaking (CSB) terms are compared with the Nolen-Schiffer (NS) anomaly regarding the energies of neighboring mirror nuclei. We find that, for a quantitative explanation of the NS anomaly, it is crucial to include CSB in partial waves with $L>0$ (besides $^1S_0$) as derived from a microscopic model for CSB of the NN interaction.Comment: 14 pages, RevTex, 2 figure

Phaseshift equivalent NN potentials and the deuteron

Different modern phase shift equivalent NN potentials are tested by evaluating the partial wave decomposition of the kinetic and potential energy of the deuteron. Significant differences are found, which are traced back to the matrix elements of the potentials at medium and large momenta. The influence of the localisation of the one-pion-exchange contribution to these potentials is analyzed in detail.Comment: 11 pages, LaTeX, 4 figures include

Single particle spectrum and binding energy of nuclear matter

In non-relativistic Brueckner calculations of nuclear matter, the self-consistent single particle potential is strongly momentum dependent. To simplify the calculations, a parabolic approximation is often used in the literature. The variation in the binding energy value introduced by the parabolic approximation is quantitatively analyzed in detail. It is found that the approximation can introduce an uncertainty of 1-2 MeV near the saturation density.Comment: 6 Latex pages, 3 postscript figure

Strange nuclear matter within Brueckner-Hartree-Fock Theory

We have developed a formalism for microscopic Brueckner-type calculations of dense nuclear matter that includes all types of baryon-baryon interactions and allows to treat any asymmetry on the fractions of the different species (n, p, $\Lambda$, $\Sigma^0$, $\Sigma^+$, $\Sigma^-$, $\Xi^-$ and $\Xi^0$). We present results for the different single-particle potentials focussing on situations that can be relevant in future microscopic studies of beta-stable neutron star matter with strangeness. We find the both the hyperon-nucleon and hyperon-hyperon interactions play a non-negligible role in determining the chemical potentials of the different species.Comment: 36 pages, LateX, includes 8 PostScript figures, (submitted to PRC

Muons and emissivities of neutrinos in neutron star cores

In this work we consider the role of muons in various URCA processes relevant for neutrino emissions in the core region of neutron stars. The calculations are done for $\beta$--stable nuclear matter with and without muons. We find muons to appear at densities $\rho = 0.15$ fm$^{-3}$, slightly around the saturation density for nuclear matter $\rho_0 =0.16$ fm$^{-3}$. The direct URCA processes for nucleons are forbidden for densities below $\rho = 0.5$ fm$^{-3}$, however the modified URCA processes with muons $(n+N\rightarrow p+N +\mu +\overline{\nu}_{\mu}, p+N+\mu \rightarrow n+N+\nu_{\mu}$), where $N$ is a nucleon, result in neutrino emissivities comparable to those from $(n+N\rightarrow p+N +e +\overline{\nu}_e, p+N+e \rightarrow n+N+\nu_e$). This opens up for further possibilities to explain the rapid cooling of neutrons stars. Superconducting protons reduce however these emissivities at densities below $0.4$ fm$^{-3}$.Comment: 14 pages, Revtex style, 3 uuencoded figs include

Cluster Formation and The Virial Equation of State of Low-Density Nuclear Matter

We present the virial equation of state of low-density nuclear matter composed of neutrons, protons and alpha particles. The virial equation of state is model-independent, and therefore sets a benchmark for all nuclear equations of state at low densities. We calculate the second virial coefficients for nucleon-nucleon, nucleon-alpha and alpha-alpha interactions directly from the relevant binding energies and scattering phase shifts. The virial approach systematically takes into account contributions from bound nuclei and the resonant continuum, and consequently provides a framework to include strong-interaction corrections to nuclear statistical equilibrium models. The virial coefficients are used to make model-independent predictions for a variety of properties of nuclear matter over a range of densities, temperatures and compositions. Our results provide constraints on the physics of the neutrinosphere in supernovae. The resulting alpha particle concentration differs from all equations of state currently used in supernova simulations. Finally, the virial equation of state greatly improves our conceptual understanding of low-density nuclear matter.Comment: 15 pages, 17 figures, minor revisions, to appear in Nucl. Phys.

Modern meson--exchange potential and superfluid neutron star crust matter

In this work we study properties of neutron star crusts, where matter is expected to consist of nuclei surrounded by superfluid neutrons and a homogeneous background of relativistic electrons. The nuclei are disposed in a Coulomb lattice, and it is believed that the structure of the lattice influences considerably the specific heat of the neutronic matter inside the crust of a neutron star. Using a modern meson--exchange potential in the framework of a local--density approximation we calculate the neutronic specific heat accounting for various shapes of the Coulomb lattice, from spherical to non--spherical nuclear shapes. We find that a realistic nucleon--nucleon potential leads to a significant increase in the neutronic specific heat with respect to that obtained assuming a uniform neutron distribution. The increase is largest for the non--spherical phase of the crust. These results may have consequences for the thermal history of young neutron stars.Comment: Revtex, 5 pages, 4 figures included as uuencoded p