Stéphane Goriely

Comprehensive nucleosynthesis analysis for ejecta of compact binary mergers

We present a comprehensive study of r-process element nucleosynthesis in the ejecta of compact binary mergers (CBMs) and their relic black-hole (BH)-torus systems. The evolution of the BH-accretion tori is simulated for seconds with a Newtonian hydrodynamics code including viscosity, pseudo-Newtonian gravity for rotating BHs, and an energy-dependent two-moment closure neutrino transport scheme. The investigated cases are guided by relativistic double neutron star (NS-NS) and NS-BH merger models. Our nucleosynthesis analysis includes the dynamical ejecta expelled during the CBM phase and the neutrino and viscously driven outflows of the relic BH-torus systems. While typically 20 25 % of the initial torus mass are lost by viscously driven outflows, neutrino-powered winds contribute at most another 1 %. Since BH-torus ejecta possess a wide distribution of electron fractions and entropies, they produce heavy elements from A 80 up to the actinides, with relative contributions of A > 130 nuclei being subdominant. The combined ejecta of CBM and BH-torus phases can reproduce the solar abundances amazingly well for A > 90. Varying contributions of the torus ejecta might account for observed variations of lighter elements with 40 < Z < 56 relative to heavier ones, and a considerable reduction of the prompt ejecta compared to the torus ejecta, e.g. in highly asymmetric NS-BH mergers, might explain the composition of heavy-element deficient stars.

Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XII: Stiffness and stability of neutron-star matter

We construct three new Hartree-Fock-Bogoliubov (HFB) mass models, labeled HFB-19, HFB20, and HFB-21, with unconventional Skyrme forces containing t4 and t5 terms, i.e., densitydependent generalizations of the usual t1 and t2 terms, respectively. The new forces underlying these models are fitted respectively to three different realistic equations of state of neutron matter for which the density dependence of the symmetry energy ranges from the very soft to the very stiff, reflecting thereby our present lack of complete knowledge of the high-density behavior of nuclear matter. All unphysical instabilities of nuclear matter, including the transition to a polarized state in neutron-star matter, are eliminated with the new forces. At the same time the new models fit essentially all the available mass data with rms deviations of 0.58 MeV and give the same high quality fits to measured charge radii that we obtained in earlier models with conventional Skyrme forces. Being constrained by neutron matter, these new mass models, which all give similar extrapolations out to the neutron drip line, are highly appropriate for studies of the r-process and the outer crust of neutron stars. Moreover, the underlying forces, labeled BSk19, BSk20 and BSk21, respectively, are well adapted to the study of the inner crust and core of neutron stars. The new family of Skyrme forces thus opens the way to a unified description of all regions of neutron stars.

Nuclear mass formula with Bogolyubov-enhanced shell-quenching: application to r-process

The ETFSI mass table, which is based entirely on microscopic forces, has been modified to take account of the strong quenching of shell effects found in HFB calculations on highly neutron-rich nuclei. The general effect of this modification is to reduce nuclear deformations; we discuss the implications for the r-process nuclidic abundances, as calculated in the canonical model.

UHE nuclei propagation and the interpretation of the ankle in the cosmic-ray spectrum

We consider the stochastic propagation of high-energy protons and nuclei in the cosmological microwave and infrared backgrounds, using revised photonuclear cross-sections and following primary and secondary nuclei in the full 2D nuclear chart. We confirm earlier results showing that the high-energy data can be fit with a pure proton extragalactic cosmic ray (EGCR) component if the source spectrum is ∝E −2.6 . In this case the ankle in the CR spectrum may be interpreted as a pair-production dip associated with the propagation. We show that when heavier nuclei are included in the source with a composition similar to that of Galactic cosmic-rays (GCRs), the pair-production dip is not present unless the proton fraction is higher than 85%. In the mixed composition case, the ankle recovers the past interpretation as the transition from GCRs to EGCRs and the highest energy data can be explained by a harder source spectrum ∝E −2.2 –E −2.3 , reminiscent of relativistic shock acceleration predictions, and in good agreement with the GCR data at low-energy and holistic scenarios.

Microscopic nuclear level densities for practical applications

Abstract New nuclear level densities based on the microscopic statistical model are proposed for practical applications. The statistical calculations are performed using the deformed Hartree–Fock–BCS predictions of the ground-state structure properties. The microscopic model includes a consistent treatment of the shell effects, pairing correlations, deformation effects and collective excitations. It predicts the experimental neutron resonance spacings with a degree of accuracy comparable to that of the phenomenological back-shifted Fermi-gas-type formulae. The microscopic level densities are renormalized to the existing experimental data, namely the s-wave neutron resonance spacings and the cumulative number of low-lying levels. Level densities for more than 8000 nuclei are made available in a table format for practical applications.

STANDARD BIG BANG NUCLEOSYNTHESIS UP TO CNO WITH AN IMPROVED EXTENDED NUCLEAR NETWORK

Primordial or big bang nucleosynthesis (BBN) is one of the three strong pieces of evidence for the big bang model together with the expansion of the universe and cosmic microwave background radiation. In this study, we improve the standard BBN calculations taking into account new nuclear physics analyses and enlarge the nuclear network up to sodium. This is, in particular, important to evaluate the primitive value of CNO mass fraction that could affect Population III stellar evolution. For the first time we list the complete network of more than 400 reactions with references to the origin of the rates, including 270 reaction rates calculated using the TALYS code. Together with the cosmological light elements, we calculate the primordial beryllium, boron, carbon, nitrogen, and oxygen nuclei. We performed a sensitivity study to identify the important reactions for CNO, 9Be, and boron nucleosynthesis. We re-evaluated those important reaction rates using experimental data and/or theoretical evaluations. The results are compared with precedent calculations: a primordial beryllium abundance increase by a factor of four compared to its previous evaluation, but we note a stability for B/H and for the CNO/H abundance ratio that remains close to its previous value of 0.7 × 10–15. On the other hand, the extension of the nuclear network has not changed the 7Li value, so its abundance is still 3-4 times greater than its observed spectroscopic value.

A Hartree-Fock-Bogoliubov mass formula

In order to have more reliable predictions of nuclear masses at the neutron drip line, we here go beyond the recent mass formula HFBCS-1 and present a new mass formula, HFB-1, based on the Hartree-Fock-Bogoliubov method. As with the HFBCS-1 mass formula, we use a 10-parameter Skyrme force along with a 4-parameter δ-function pairing force and a 2-parameter phenomenological Wigner term. However, with the original HFBCS-1 Skyrme force (MSk7), the rms error becomes unacceptably large and a new force fit is required. With the isoscalar and isovector effective masses constrained to be equal, the remaining 15 degrees of freedom are fitted to the masses of all the 1754 measured nuclei with A ≥ 16, N - Z > 2 given in the 1995 Audi-Wapstra compilation. The rms error with respect to the masses of all the 1888 measured nuclei with Z, N ≥ 8 is 0.764 MeV. A complete mass table, HFB-1 (available on the Web), has been constructed, giving all nuclei lying between the two drip lines over the range Z, N ≥ 8 and Z ≤ 120. A comparison between HFB-1 and HFBCS-1 mass tables shows that the HFBCS model is a very good approximation of the HFB theory, in particular for masses, the extrapolated masses never differing by more than 2 MeV below Z ≤ 110. We also find that the behaviour of shell gaps far away from the region of beta stability does not depend on whether the HFBCS or HFB methods are used, in particular, no quenching of astrophysical interest arises from replacing the BCS method by the Bogoliubov method.

Improved predictions of nuclear reaction rates with the TALYS reaction code for astrophysical applications

Context. Nuclear reaction rates of astrophysical applications are traditionally determined on the basis of Hauser-Feshbach reaction codes. These codes adopt a number of approximations that have never been tested, such as a simplified width fluctuation correction, the neglect of delayed or multiple-particle emission during the electromagnetic decay cascade, or the absence of the pre-equilibrium contribution at increasing incident energies. Aims. The reaction code TALYS has been recently updated to estimate the Maxwellian-averaged reaction rates that are of astrophysical relevance. These new developments enable the reaction rates to be calculated with increased accuracy and reliability and the approximations of previous codes to be investigated. Methods. The TALYS predictions for the thermonuclear rates of relevance to astrophysics are detailed and compared with those derived by widely-used codes for the same nuclear ingredients. Results. It is shown that TALYS predictions may differ significantly from those of previous codes, in particular for nuclei for which no or little nuclear data is available. The pre-equilibrium process is shown to influence the astrophysics rates of exotic neutron-rich nuclei significantly. For the first time, the Maxwellian-averaged (n, 2n) reaction rate is calculated for all nuclei and its competition with the radiative capture rate is discussed. Conclusions. The TALYS code provides a new tool to estimate all nuclear reaction rates of relevance to astrophysics with improved accuracy and reliability.

Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas: II. Role of the effective mass

We have constructed four new complete mass tables, referred to as (Hartree-Fock-Bogoliubov) HFB-4 to HFB-7, each one including all the 9200 nuclei lying between the two drip lines over the range of

Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. III: Role of particle-number projection

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