Original article can be found at: http://www.nature.com/nature/index.html--Copyright Nature Publishing Group --DOI : 10.1038/nature0345

We present calculations of r-process nucleosynthesis in neutrino-driven winds from the nascent neutron stars of core-collapse supernovae. A full dynamical reaction network for both the α-rich freezeout and the subsequent r-process is employed. The physical properties of the neutrino-heated ejecta are deduced from a general relativistic model in which spherical symmetry and steady flow are assumed. Our results suggest that protoneutron stars with a large compaction ratio provide the most robust physical conditions for the r-process. The third peak of the r-process is well reproduced in the winds from these "compact" proto-neutron stars even for a moderate entropy, ∼ 100 − 200N A k, and a neutrino luminosity as high as ∼ 10 52 ergs s −1 . This is due to the short dynamical timescale of material in the wind. As a result, the overproduction of nuclei with A ∼ < 120 is diminished (although some overproduction of nuclei with A ≈ 90 is still evident). The abundances of the r-process elements per event is significantly higher than in previous studies. The total-integrated nucleosynthesis yields are in good agreement with the solar r-process abundance pattern. Our results have confirmed that the neutrino-driven wind scenario is still a promising site in which to form the solar r-process abundances. However, our best results seem to imply both a rather soft neutron-star equation of state and a massive proto-neutron star which is difficult to achieve with standard corecollapse models. We propose that the most favorable conditions perhaps require that a massive supernova progenitor forms a massive proto-neutron star by accretion after a failed initial neutrino burst.

We study the astrophysical reaction rate for the formation of 9 Be through the three body reaction α(αn, γ). This reaction is one of the key reactions which could bridge the mass gap at A = 8 nuclear systems to produce intermediate-to-heavy mass elements in alpha-and neutron-rich environments such as r-process nucleosynthesis in supernova explosions, s-process nucleosynthesis in asymptotic giant branch (AGB) stars, and primordial nucleosynthesis in baryon inhomogeneous cosmological models. To calculate the thermonuclear reaction rate in a wide range of temperatures, we numerically integrate the thermal average of cross sections assuming a two-steps formation through a metastable 8 Be, α + α ⇀ ↽ 8 Be(n,γ) 9 Be. Off-resonant and on-resonant contributions from the ground state in 8 Be are taken into account. As input cross section, we adopt the latest experimental data by photodisintegration of 9 Be with laser-electron photon beams, which covers all relevant resonances in 9 Be. Experimental data near the neutron threshold are added with γ-ray flux corrections and a new least-squares analysis is made to deduce resonance parameters in the Breit-Wigner formulation. Based on the photodisintegration cross section, we provide the reaction rate for α(αn, γ) 9 Be in the temperature range from T 9 =10 −3 to T 9 =10 1 (T 9 is the temperature in units of 10 9 K) both in the tabular form and in the analytical form for potential usage in nuclear reaction network calculations.The calculated reaction rate is compared with the reaction rates of the CF88 and the NACRE compilations. The CF88 rate, which is based on the photoneutron cross section for the 1/2 + state in 9 Be by Berman et al., is valid at T 9 > 0.028 due to lack of the off-resonant contribution. The CF88 rate differs from the present rate by a factor of two in a temperature range T 9 ≥ 0.1. The NACRE rate, which adopted different sources of experimental information on resonance states in 9 Be, is 4-12 times larger than the present rate at T 9 ≤ 0.028, but is consistent with the present rate to within ±20% at T 9 ≥ 0.1. 2

The neutrino-nucleus reaction cross sections of 4 He and 12 C are evaluated using new shell model Hamiltonians. Branching ratios of various decay channels are calculated to evaluate the yields of Li, Be, and B produced through the -process in supernova explosions. The new cross sections enhance the yields of

There has been a persistent conundrum in attempts to model the nucleosynthesis of heavy elements by rapid neutron capture (the r-process). Although the location of the abundance peaks near nuclear mass numbers 130 and 195 identify an environment of rapid neutron capture near closed nuclear shells, the abundances of elements just above and below those peaks are often underproduced by more than an order of magnitude in model calculations. At the same time there is a debate in the literature as to what degree the r-process elements are produced in supernovae or the mergers of binary neutron stars. In this paper we propose a novel solution to both problems. We demonstrate that the underproduction of nuclides above and below the r-process peaks in main or weak r-process models (like magnetohydrodynamic jets or neutrino-driven winds in core-collapse supernovae) can be supplemented via fission fragment distributions from the recycling of material in a neutron-rich environment such as that encountered in neutron star mergers. In this paradigm, the abundance peaks themselves are well reproduced by a moderately neutron rich, main r-process environment such as that encountered in the magnetohydrodynamical jets in supernovae supplemented with a high-entropy, weakly neutron rich environment such as that encountered in the neutrino-driven-wind model to produce the lighter r-process isotopes. Moreover, we show that the relative contributions to the r-process abundances in both the solar-system and metal-poor stars from the weak, main, and fission-recycling environments required by this proposal are consistent with estimates of the relative Galactic event rates of core-collapse supernovae for the weak and main r-process and neutron star mergers for the fission-recycling r-process.

Neutrino-induced reactions on 16 O are investigated by shell-model calculaions with new shellmodel Hamiltonians, which can describe well the structure of p-shell and p-sd shell nuclei. Distribution of the spin-dipole strengths in 16 O, which give major contributions to the ν-16 O reaction cross sections, is studied with the new Hamiltonians. Muon-capture reaction rates on 16 O are also studied to discuss the quenching of the axial-vector coupling in nuclear medium. Charged-current and neutral-current reaction cross sections are evaluated in various particle and γ emission channels as well as the total ones at neutrino energies up to E ν ≈ 100 MeV. Branching ratios for the various channels are obtained by the Hauser-Feshbach statistical model calculations, and partial cross sections for single-and multi-particle emission channels are evaluated. The cross sections updated are compared with previous continuum random phase approximation (CRPA) calculations. Effects of multi-particle emission channels on nucleosynthesis in core-collapse supernova (SN) explosions are investigated. Inclusion of αp emission channels is found to lead to an enhancement of production yields of 11 B and 11 C through 16 O (ν, ν' αp) 11 B and 16 O (ν, e − αp) 11 C reactions, respectively. Study of neutrino-nucleus reactions at neutrino energies up to E ν =100 MeV is an important subject for the detection of supernova (SN) neutrinos. Several nuclear targets such as 12 C, 16 O and 40 Ar are especially of interest from the point of view of their availability. Accurate evaluation of the ν-induced cross sections is crucial for the study of neutrino production and nucleosythesis in SN explosions as well as neutrino oscillation properties. Recently, new shell-model Hamiltonians become available due to the development of the study of exotic nuclei. Important roles of the tensor interaction are taken into account in the new Hamiltonians, so that they can explain shell evolutions and change of magic numbers toward driplines [1, 2]. Spin modes of nuclei such as Gamow-Teller (GT) transtions, magnetic dipole transitions and moments are found to be well described by these Hamiltonians. Neutrino-induced reaction cross sections on 12 C have been evaluated with a new p-shell Hamiltonian, SFO [3], which can reproduce the GT transition strength in 12 C. The SFO is constructed to be used in p-sd shell with the inclusion of excitations of p-shell nucleons to sd-shell up to 2-3 ω configurations. Exclusive and inclusive charged-and neutral-current reaction cross setions for DAR (decay-at-rest) ν's are found to be well reproduced by the SFO within experimental error bars [4, 5]. Cross sections for particle emission channels obtained by Hauser-Feshbach method are used to study nucleosynthesis of light elements in SN explosions [4,6]. Production yields of 7 Li and 11 B are found to be enhanced compared with previous calculations [7]. In case of MSW (Mikheyev-Smirnov-Wolfenstein) resonance ν oscillations, the yield ratio of 7 Li/ 11 B is pointed out to be a good measure...

We present the newest statistical and numerical analysis of the matter and cosmic microwave background power spectrum with effects of the primordial magnetic field (PMF) included. New limits to the PMF strength and power spectral index are obtained based upon the accumulated data for both the matter and CMB power spectra on small angular scales. We find that a maximum develops in the probability distribution for a magnitude of the PMF of jB j ¼ 0:85 AE 1:25ðAE1Þ nG on a comoving scale of at 1 Mpc, corresponding to upper limits of <2:10 nG (68% CL) and <2:98 nG (95% CL). While for the power spectral index we find n B ¼ À2:37 þ0:88 À0:73 ðAE1Þ, corresponding to upper limits of < À 1:19 (68% CL) and < À 0:25 (95% CL). This result provides new constraints on models for magnetic field generation and the physics of the early universe. We conclude that future observational programs for the CMB and matter power spectrum will likely provide not only upper limits but also lower limits to the PMF parameters.

The rapid neutron-capture process (r-process) is a major process to synthesize elements heavier than iron, but the astrophysical site(s) of r-process is not identified yet. Neutron star mergers (NSMs) are suggested to be a major r-process site from nucleosynthesis studies. Previous chemical evolution studies however require unlikely short merger time of NSMs to reproduce the observed large starto-star scatters in the abundance ratios of r-process elements relative to iron, [Eu/Fe], of extremely metal-poor stars in the Milky Way (MW) halo. This problem can be solved by considering chemical evolution in dwarf spheroidal galaxies (dSphs) which would be building blocks of the MW and have lower star formation efficiencies than the MW halo. We demonstrate that enrichment of r-process elements in dSphs by NSMs using an N -body/smoothed particle hydrodynamics code. Our highresolution model reproduces the observed [Eu/Fe] by NSMs with a merger time of 100 Myr when the effect of metal mixing is taken into account. This is because metallicity is not correlated with time up to ∼ 300 Myr from the start of the simulation due to low star formation efficiency in dSphs. We also confirm that this model is consistent with observed properties of dSphs such as radial profiles and metallicity distribution. The merger time and the Galactic rate of NSMs are suggested to be 300 Myr and ∼ 10 −4 yr −1 , which are consistent with the values suggested by population synthesis and nucleosynthesis studies. This study supports that NSMs are the major astrophysical site of r-process.