Meson Production at COSY-TOF and COSY-ANKE

The roles of the COSY-TOF and COSY-ANKE spectrometers in the measurement of strange meson production are briefly reviewed, mainly in connection with new results on the pp -> K^+ p Lambda, pp -> K^+ p Sigma^0 and pp -> K^+ n Sigma^+ reactions.Comment: Invited talk at the MESON2010 conference in Krakow, June 201

Relativistic Mean Field calculations of nuclear properties in early stages of stellar collapse

We use the Relativistic Mean Field (RMF) method to calculate properties of neutron rich, usually deformed nuclei, important for equation of state calculations and which have significant abundance in the early stages of stellar collapse. We compare the results of our microscopic calculations with existing cold nuclear equations of state based on macroscopic liquid drop model and the FRLDM model.Comment: 4 pages , Latex, 4 figures, uses espcrc1.sty. To appear in Nucl. Phys. A, proceedings of "Nuclei in the Cosmos 1996" 4th International Symposium on Nuclear Astrophysics. e-mail contact: [email protected]

Conditions for Shock Revival by Neutrino Heating in Core-Collapse Supernovae

Energy deposition by neutrinos can rejuvenate the stalled bounce shock and can provide the energy for the supernova explosion of a massive star. This neutrino-heating mechanism, however, is not finally accepted or proven as the trigger of the explosion. Part of the problem is that the complexity of the hydrodynamic models often hampers a clear and simple interpretation of the results. This demands a deeper theoretical understanding of the requirements of a successful shock revival. A toy model is presented here for discussing the neutrino heating phase analytically by a time-dependent treatment, which allows one to calculate the radius and velocity of the supernova shock from global properties of the gain layer as solutions of an initial value problem. A criterion is derived for the requirements of shock revival. It confirms the existence of a minimum neutrino luminosity needed for shock expansion, but also demonstrates the importance of a sufficiently large mass infall rate to the shock. The possibility of very energetic neutrino-driven explosions seems excluded because the total specific energy transferred to nucleons is limited by about 1e52 ergs per solar mass (about 5 MeV per nucleon) and the total mass in the gain layer is typically only around 0.1 solar masses. Energy transport by convection from the region of maximum heating to radii closer behind the shock is found to support the explosion by reducing the energy loss associated with the inward advection of neutrino-heated matter through the gain radius. (abridged)Comment: 36 pages, A&A LaTeX, 14 eps figures, major extensions due to referee comments; accepted by Astronomy & Astrophysic

Muon Bremsstrahlung and Muonic Pair Production in Air Showers

The objective of this work is to report on the modifications in air shower development due to muon bremsstrahlung and muonic pair production. In order to do that we have implemented new muon bremsstrahlung and muonic pair production procedures in the AIRES air shower simulation system, and have used it to simulate ultra high energy showers in different conditions. The influence of the mentioned processes in the global development of the air shower is important for primary particles of large zenith angles, while they do not introduce significant changes in the position of the shower maximum.Comment: To be presented at the International Symposium on Very High Energy Cosmic Ray Interactions X

Systematic thermal reduction of neutronization in core-collapse supernovae

We investigate to what extent the temperature dependence of the nuclear symmetry energy can affect the neutronization of the stellar core prior to neutrino trapping during gravitational collapse. To this end, we implement a one-zone simulation to follow the collapse until beta equilibrium is reached and the lepton fraction remains constant. Since the strength of electron capture on the neutron-rich nuclei associated to the supernova scenario is still an open issue, we keep it as a free parameter. We find that the temperature dependence of the symmetry energy consistently yields a small reduction of deleptonization, which corresponds to a systematic effect on the shock wave energetics: the gain in dissociation energy of the shock has a small yet non-negligible value of about 0.4 foe (1 foe = 10^51 erg) and this result is almost independent from the strength of nuclear electron capture. The presence of such a systematic effect and its robustness under changes of the parameters of the one-zone model are significative enough to justify further investigations with detailed numerical simulations of supernova explosions.Comment: 15 pages, 2 tables, 3 figure

Electro-disintegration following beta-decay

I show that the disintegration of weakly-bound nuclei and the ionization of weakly-bound atomic electrons due to their interaction with leptons from beta decay is a negligible effect.Comment: 3 pages, 1 figure, to be published in the Physical Review

Relativistic corrections to the long range interaction between closed shell atoms

The complete $O(\alpha^2)$ correction to the long range interaction between neutral closed shell atoms is obtained, the relation to the asymptotic expansion of the known short range interaction at the atomic scale is presented and a general interaction potential which is valid in the whole range of the inter atomic distances is constructed.Comment: 9 pages, accepted for Phys. Rev.

Modeling interactions for resonant p-wave scattering

In view of recent experiments on ultra-cold polarized fermions, the zero-range potential approach is generalized to situations where two-body scattering is resonant in the p-wave channel. We introduce a modified scalar product which reveals a deep relation between the geometry of the Hilbert space and the interaction. This formulation is used to obtain a simple interpretation for the transfer rates between atomic and molecular states within a two branches picture of the many-body system close to resonance. At resonance, the energy of the dilute gas is found to vary linearly with density.Comment: 4 page