Pierre M. Pizzochero

ANGULAR MOMENTUM TRANSFER IN VELA-LIKE PULSAR GLITCHES

The angular momentum transfer associated with Vela-like glitches has never been calculated directly within a realistic scenario for the storage and release of superfluid vorticity; therefore, the explanation of giant glitches in terms of vortices has not yet been tested against observations. We present the first physically reasonable model, both at the microscopic and macroscopic level (spherical geometry, n = 1 polytropic density profile, density-dependent pinning forces compatible with vortex rigidity), to determine where in the star the vorticity is pinned, how much of it is pinned, and for how long. For standard neutron star parameters (M = 1.4 M ?, Rs = 10?km, ?Hz?s?1), we find that maximum pinning forces of order fm 1015?dyn?cm?1 can accumulate ?L gl 1040?erg?s of superfluid angular momentum, and release it to the crust at intervals ?t gl 3 years. This estimate of ?L gl is one order of magnitude smaller than that implied indirectly by current models for post-glitch recovery, where the core and inner-crust vortices are taken as physically disconnected; yet, it successfully yields the magnitudes observed in recent Vela glitches for both jump parameters, ??gl and , provided one assumes that only a small fraction (<10%) of the total star vorticity is coupled to the crust on the short timescale of a glitch. This is reasonable in our approach, where no layer of normal matter exists between the core and the inner-crust, as indicated by existing microscopic calculation. The new scenario presented here is nonetheless compatible with current post-glitch models.

Neutrino capture cross sections for 40Ar and β-decay of 40Ti

Abstract Shell-model calculations of solar neutrino absorption cross sections for 40Ar, the proposed component of the ICARUS detector, are presented. It is found that low-lying Gamow-Teller transitions lead to a significant enhancement of the absorption rate over that expected from the Fermi transition between the isobaric analog states, leading to an overall absorption cross section for 8B neutrinos of (11.5 ± 0.7) × 10−43 cm2 or a total expected rate of 6.7 ± 2.5 SNU. We also note that the pertinent Gamow-Teller transitions in 40Ar are experimentally accessible from the β-decay of the mirror nucleus 40Ti. Predictions for the branching ratios to states in 40Sc are presented, and the theoretical halflife of 55 ± 5 ms is found to be in good agreement with the experimental value of 56−12+18 ms.

Systematic thermal reduction of neutronization in core-collapse supernovae

Abstract 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 β-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 significant enough to justify further investigations with detailed numerical simulations of supernova explosions.

PINNING AND BINDING ENERGIES FOR VORTICES IN NEUTRON STARS: COMMENTS ON RECENT RESULTS

We investigate when the energy that pins a superfluid vortex to the lattice of nuclei in the inner crust of neutron stars can be approximated by the energy that binds the vortex to a single nucleus. Indeed, although the pinning energy is the quantity relevant to the theory of pulsar glitches, so far full quantum calculations have been possible only for the binding energy. Physically, the presence of nearby nuclei can be neglected if the lattice is dilute, namely with nuclei sufficiently distant from each other. We find that the dilute limit is reached only for quite large Wigner-Seitz cells, with radii > 55 fm; these are found only in the outermost low-density regions of the inner crust. We conclude that present quantum calculations do not correspond to the pinning energies in almost the entire inner crust and thus their results are not predictive for the theory of glitches.

Nuclear energy functional with a surface-peaked effective mass: global properties

A correction to the nuclear functional is proposed in order to improve the density of states around the Fermi surface. The induced effect of this correction is to produce a surface-peaked effective mass, whose mean value can be tuned to get closer to 1 for the states close to the Fermi energy. In this work we study the effect of the correction term on the global properties of nuclei such as the density of states in 40Ca and 208Pb, pairing and specific heat at low temperature in 120Sn. In the latter application, an explicit temperature-dependent form of the correction term is employed and it is shown that the critical temperature is reduced by 40–60 keV.

The solar neutrino capture cross section for 23Na

Abstract A coincidence (electron, γ-ray) experiment designed to identify one or more components of the solar neutrino spectrum has been proposed based on a large array of NaBr detectors. In support of the design of this detector, we calculate the solar neutrino absorption rate for v + 23 Na → 23 Mg + e − within the Standard Solar Model making use of both experimental and theoretical data for the structure of the two nuclei involved. It is found that the inclusion of excited states in 23Mg enhances the absorption cross section by ≈30%, with approximately one third of this enhancement coming from excited states for which experimental data does not exist. The solar neutrino absorption rate is calculated to be 3.5 ± 1.3 SNU, which amounts to about one count every six days for the proposed detector.

Effects of the temperature dependence of the in-medium nucleon mass on core-collapse supernovae

Aims. A complete description of the core collapse supernova mechanism requires an appropriate treatment of both the hydrodynamics and the microphysics. We study the influence of a nuclear physics input, namely the temperature dependence of the nucleon effective mass in nuclei induced by the in-medium effects, in the core collapse of a massive star. Methods. We present here the first implementation of this nuclear input in a hydrodynamical one-dimensional simulation. The simulations are performed with a spherically symmetric Newtonian model, with neutrino transport treated in the multi-group flux-limited diffusion approximation. Results. The inclusion of the temperature dependence of the in-medium nucleon mass has an impact on the equation of state of the system and reduces the deleptonisation during the collapse. This results in a non-negligible effect on the shock wave energetics. The shock wave is formed more outwards, and in the first few milliseconds after bounce the shock front has propagated further out.