Origin of Matter and Evolution of Galaxies 2003

PREFACE

CONTENTS

The brane-world paradigm is based upon the premise that our universe could be a submanifold embedded in a higher-dimensional spacetime. In the currently popular Randall-Sundrum model, the universe is described as a three-space (3-brane) embedded in a five-dimensional anti-de Sitter spacetime with a large (infinite) extra dimension. This concept is motivated by the D-brane solution found in ten-dimensional superstring theory and eleven dimensional M-theory/supergravity. If correct, this notion significantly alters our views on the origin of matter and origin of galaxies. This talk summarizes some possible observational consequences of brane-world cosmology For example, a new “dark radiation“ term arises in the cosmic evolution equations which can affect the radiation dominated epoch. Moreover, matter may literally disappear into (or reemerge from) the extra dimension. This suggests a new interpretations for dark matter, dark energy and their evolution. Further possible consequences of brane-world cosmology are time-varying physical constants and the existence of a sub-horizon compact dimension. Constraints on these possibilities arise from big-bang and stellar nucleosynthesis, observations of high redshift supernovae, galaxy-clusters, X-ray gas in galactic clusters, and the cosmic microwave background. So far, all of the available constraints are consistent with (and may even slightly favor) the existence of a large extra dimension.

From the observations of the anisotropies of the Cosmic Microwave Background (CMB) radiation, the WMAP satellite has provided a determination of the baryonic density of the Universe, Ω_bh², with an unprecedented precision. This imposes a careful reanalysis of the standard Big-Bang Nucleosynthesis (SBBN) calculations. We have updated our previous calculations using thermonuclear reaction rates provided by a new analysis of experimental nuclear data constrained by R-matrix theory. Combining these BBN results with the Ω_bh² value from WMAP, we deduce the light element (⁴He, D, ³He and ⁷Li) primordial abundances and compare them with spectroscopic observations. There is a very good agreement with deuterium observed in cosmological clouds, which strengthens the confidence on the estimated baryonic density of the Universe. However, there is an important discrepancy between the deduced ⁷Li abundance and the one observed in halo stars of our Galaxy, supposed, until now, to represent the primordial abundance of this isotope. The origin of this discrepancy, observational, nuclear or more fundamental remains to be clarified. The possible role of the up to now neglected ⁷Be(d,p)2α and ⁷Be(d,α)⁵Li reactions is considered.

We re-formulate the theory of cosmological perturbations in decaying cold dark matter cosmology and calculate cosmological microwave background anisotropies. By comparing with recent observation we derive a new bound on the life time of such decaying particles. We show that the data of CMB anisotropies alone do not prefer the decaying cold dark matter models to the standard cold dark matter ones, and constrained to Г ⁻¹ ≥ 43 Gyr at 3σ.

In this talk, we consider the effects on big bang nucleosynthesis (BBN) of the hadronic decay of a long-lived massive particle in supergravity. If high-energy hadrons are emitted during/after the BBN epoch (t ~ 10⁻² – 10¹² sec), they may change the abundances of the light elements through the destruction processes caused by such high energy hadrons, which may result in a significant discrepancy between standard BBN and observation. So far, these types of hadronic decay process in BBN have not been studied well without a few papers whose treatments were simple, because of severe shortage of hadron experimental data. However, recently the experiments of the high energy physics have been widely developed. Now we can obtain a lot of experimental informations of the hadron fragmentation in the high energy region and also simulate the process even in the higher energies where we have no experimental data by executing the numerical code of the hadron fragmentation, e.g. JETSET 7.4 Monte Carlo event generator. In addition, we have more experimental data of the hadron-nucleon cross sections. One of the candidates of the long-lived massive particle would be gravitino which appears in supergravity. If we consider general particle physics models in supergravity, it possibly decays during/after big-bang nucleosynthesis epoch. Compared with observational light element abundances, for the successful nucleosynthesis, we can obtain severe upper bound on reheating temperature after the primordial inflation which controls the primordial abundance of gravitinos. We discuss the implications of that result for cosmology, particle physics and nuclear physics.

With gamma-ray measurements from the decay of radioactive isotopes of intermediate lifetimes, nucleosynthesis in stars, supernovae, and novae may be constrained. ESA’s INTEGRAL observatory with its Ge spectrometer SPI is now in orbit for one year, and at least four more years are scheduled. The INTEGRAL satellite and instruments show excellent performance. Instrumental background, higher than, estimated, limits current gamma-ray line results. Nevertheless, first results on annihilation radiation and ²⁶Al demonstrate the potential of this mission for nuclear astrophysics. The ²⁶Al line is narrow, casting doubt on previously-reported broadening which would require typical ²⁶Al decay at ≃ 500 km s⁻¹; the annihilation of e⁺ appears concentrated in the inner Galaxy, more extended than what would correspond to the Galactic bulge, but without a significant Galactic-disk component. After its first successful mission year with emphasis on hard-X-ray sources, the second mission year is aimed more at the study of nucleosynthesis sources, with their required long exposures.

Presolar SiC grains of the types mainstream, Y, and Z are believed to have formed in thermally pulsing asymptotic giant branch stars with a range of metallicity: mainstream grains in stars of close-to-solar metallicity, Y grains in stars of around half-solar metallicty, and Z grains in stars of around one-third solar metallicity. From their Si and Ti isotopic ratios, it is possible to obtain information on both neutron capture processes that take place in the He intershell and initial compositions of the parent stars of the grains. Since Z grains formed in stars with the lowest metallicity, their study will likely provide insight into the Galactic chemical evolution of these elements as well as nuclear processes in low-metallicity stars. A preliminary comparison of data on Z grains with models of AGB stars confirms that Z grains formed in low-metallicity stars (Z≤0.006). The ¹²C/¹³C ratios of the Z grains indicate that in these stars cool bottom processing operates during the third dredge-up.

Based on XMM-Newton observations of the X-ray halo of M 87 and the Centaurus cluster, abundance profiles of O, Mg, Si, and Fe of the intracluster medium (ICM) are derived. The abundances of Si and Fe show strong decreasing gradients. In contrast, the O and Mg abundances are about a half of the Si abundance at the center. From the gas mass to stellar mass ratio and the comparison of Mg abundance with the stellar metallicity, the stellar mass loss from the central galaxies is indiated to be the main source of the gas in the very central region of the clusters. The observed O, Si and Fe abundance pattern determines the contribution of supernova (SN) Ia and SN II, with the abundance pattern of ejecta of SN Ia. The most of Si and Fe of the ICM in the central region of the clusters come from SN Ia occured in the central galaxies. In order to explain the observed O/Si ratio of a half solar, SN Ia products should have similar abundances of Si and Fe, which may reflect dimmer SN Ia observed in old stellar systems. The Mg/O ratio are close to those of Galactic stars, which indicates that nucleosynthesis of these elements has no discrepancy between our Galaxy and early-type galaxies.

The advent of 8-10m class telescopes equipped with very efficient and high resolution spectrographs has strongly boosted the study of chemical patterns in the Galactic halo, allowing us to derive very accurate abundances in the most metal-poor stars. Here, the tremendous progress recently achieved in this field of research is presented and critically reviewed.

Observed large dispersions in chemical abundances of metal-poor stars may indicate that the inter-stellar gas was not mixed enough at the early epoch. We construct an inhomogeneous chemical evolution model, and compare predicted stellar abundance distributions with observations, using statistical method. We take several supernova yields; the data of Nomoto et al. (1997) and Woosley & Weaver (1995), and discuss consistency of these yield sets with observations. In particular, we discuss the origin of r-process, from the point of view of enrichment of europium. Using the Subaru HDS, we have estimated Eu abundances of three extremely metal-poor stars with [Fe/H] ≳ -3. Comparison with our Galactic evolution model implies the dominant source of Eu to be the low-mass end of the supernova mass range.

Recent developments in solar, reactor, and accelerator neutrino physics are reviewed. Implications for neutrino physics, solar physics, nuclear two-body physics, and r-process nucleosynthesis are briefly discussed.

Future experiments of double beta decays(DBD) for studying neutrino masses are briefly reported. Neutrino-less double beta decays(0νββ decays) provide an evidence for the Majorana nature of neutrinos and an absolute ν mass scale. In view of recent ν oscillation studies, high sensitive studies of 0νββ decays with mass sensitivities of the solar and atmospheric ν masses are of great interest. Future 0νββ experiments with a mass sensitivity of m_ν = 10 ~ 50 meV have been proposed, and their R&D works are under progress. International cooperative works are encouraged for new generation 0νββ experiments.

We, the Tokyo group, have performed some dark matter search experiments at an underground cell in the Kamioka Observatory (2700 m.w.e). Two cryogenic detectors, a 168-g lithium fluoride (LiF) bolometer and a 176-g sodium fluoride (NaF) bolometer, are aimed at the direct detection of nuclear recoils caused by elastic scattering of weakly interacting massive particles (WIMPs) through a spin-dependent interaction. The LiF bolometer run at Kamioka was performed from 2001 through 2002 with the total exposure of 4.1 kg days, and the NaF bolometer run was performed from 2002 through 2003 with the total exposure of 3.38 kg days. From these experiments, we derived limits on WIMP-nucleon couplings in the a_p-a_n parameter plane which is complementary to other existing limits. We are also developing a direction-sensitive detector using organic crystal scintillator in order to sense the wind of WIMP dark matter. It exploits the anisotropic scintillation efficiency of organic crystals with respect to the direction of nuclear recoils relative to crystallographic axes. A variation of about 7% was observed in the scintillation efficiency of carbon recoils in a stilbene crystal for recoil energy of 30 keV to 1 MeV using neutrons from ⁷Li(p, n)⁷Be and ²⁵²Cf. We are now performing a pilot experiment at Kamioka to prove the feasibility of this method.

We have estimated fluxes of neutrinos and gamma-rays that are generated from decays of charged and neutral pions from a pulsar surrounded by supernova ejecta in our galaxy, including an effect that has not been taken into consideration, that is, interactions between high energy cosmic rays themselves in the nebula flow, assuming that hadronic components are the energetically dominant species in the pulsar wind. Bulk flow is assumed to be randomized by passing through the termination shock and energy distribution functions of protons and electrons behind the termination shock are assumed to obey the relativistic Maxwellians. We have found that fluxes of neutrinos and gamma-rays depend very sensitively on the wind luminosity, which is assumed to be comparable to the spin-down luminosity. In the case where B = 10¹²G and P = 1ms, neutrinos should be detected by km³ high-energy neutrino detectors such as AMANDA and IceCube. Also, gamma-rays should be detected by Cherenkov telescopes such as CANGAROO and H.E.S.S. as well as by gamma-ray satellites such as GLAST.

Asymptotic normalization coefficients (ANCs) have proven to be useful for determining reaction rates of interest in nuclear astrophysics. These coefficients, which provide the normalization of the tail of the overlap function, determine S factors for direct capture reactions at astrophysical energies. They also can be related to resonance capture rates and are particularly useful for determining proton-capture reaction rates that involve subthreshold resonance states. During the past eight years, many ANCs have been measured by peripheral transfer reactions. Recent proton transfer reaction measurements have yielded ANCs for ¹⁴O → ¹³N + p, ¹⁵O → ¹⁴N + p and ²¹Na → ²⁰Ne + p. These results have been used to find S factors for ¹³N(p,γ)¹⁴O, ¹⁴N(p,γ)¹⁵O and ²⁰Ne(p,γ)²¹Na. Using mirror symmetry, the ¹³C(⁷Li,⁸Li)¹²C reaction has been used to obtain a new measurement of the ANC that defines the S factor for ⁷Be(p,γ)⁸B. Following an introduction to ANCs, the recent experiments are discussed along with the astrophysical implications of these measurements.

The neutron capture reaction on ¹⁴C leading to the ¹⁵C ground state, which is important in the nucleo-synthesis processes in the universe, has been studied by using the Coulomb dissociation of ¹⁵C on a Pb target at 68 MeV/nucleon. The dissociation cross sections at large impact parameters over 20 fm has been translated into the energy spectrum of the neutron capture by using the principle of the detailed balance. The energy spectrum shows the typical p-wave capture characteristics, which is understood by the fact that the ground state of ¹⁵C is a loosely bound halo state. The present study suggests that such a p-wave neutron capture may often occur at the very neutron rich regions, where important nucleo-synthesis paths are expected.

We calculate nucleosynthesis in Population (Pop) III supernovae (SNe) and compare the yields with various abundance patterns of extremely metal-poor (EMP) stars. We assume that the observed EMP stars are the second generation stars, which have the metal-abundance pattern of the Pop III SNe. Previous theoretical yields and observations do not match well, suggesting that the simplest supernova model cannot account for the observations. In this paper we consider high energy explosions, “low-density” explosions, and mixing-fallback models. We show that the abundance patterns of both C-normal and C-rich EMP stars with [Fe/H] ≲ - 2.5 can be well reproduced with the yield of core-collapse SNe of M ~ 20 - 130M⊙. The abundance patterns of the [Fe/H] ~ −2.5 stars correspond to supernova yields with normal explosion energies, while those of the C-normal ([C/Fe] < 1) stars with [Fe/H] ≃ −4 ~ −3 correspond to high-energy supernova yields. The abundance pattern of C-rich [C/Fe] ≳ 2) low [Fe/H] (≃ - 5 ~ - 3.5) stars can be explained with the faint SN yield with little ⁵⁶Ni ejection, which is similar to SN1997D. Even we vary parameters, we still need a large explosion energy to obtain the large Co/Fe and Zn/Fe ratios observed in typical EMP stars.

We calculate evolution, explosion and nucleosynthesis of population III very-massive stars with 500 and 1000M⊙. Then we compare the results of nucleosynthesis with the abundance patterns of hot gases in M82, intracluster matter (ICM), and extremely metal-poor stars in the Galactic halo. The patterns of nucleosynthesis match the observational data in M82, that is, undersolar [O/Fe], [Ne/Fe] and solar values or oversolar [Mg/Fe], [Si/Fe], and [S/Fe] if the contribution of the jet material is not so large. For the halo stars, [O/Fe] in our models are smaller than the observational abundances, but more detailed observations at [Fe/H] ≲ -3 are needed to judge whether pop III very-massive stars contributes to the early Galactic chemical evolution or not.

The basic features of the Trojan Horse Method are discussed together with a review of recent applications aimed to extract the bare S_b(E) astrophysical factor for several two body processes. In this framework information on electron screening potential U_e was obtained from comparison with the direct experiments of fusion reactions.

We present the s-process nucleosynthesis in massive stars with a wide range of metallicity, using the recent sets of reaction rates and stellar input physics. The decreasing metallicity makes poisoning effects of primary ¹⁶O larger at the late phase of core He burning, at which the s-process occurs actively in solar metallicity stars, and prevents the synthesis of heavy elements from being efficient. However, we find that the s-process proceeds very efficiently via neutron source reaction of ¹³C(α,n)¹⁶O at the end of core H burning phase when the metallicity decreases below Z ~ 10⁻⁸. These massive, extremely low metallicity stars may have an important contribution of light s-elements to observed extremely metal-poor stars.

A ¹⁸⁷Os-¹⁸⁷Re pair has been known to be a good cosmochronometer for the r-process nucleosynthesis. The radioactivity ¹⁸⁷Re decays to a daughter nucleus ¹⁸⁷Os with a half-life of 2.0 × 10⁵ years. The ¹⁸⁷Re has been considered to be synthesized predominantly by the r-process, whereas the ¹⁸⁷Os has been produced by both the radioactive decay of ¹⁸⁷Re and the s-process nucleosynthesis. The s-process contaminations to ¹⁸⁷Re and ¹⁸⁷Os must be subtracted for an estimation of the passing time from a r-process episode to the present time with an accuracy. An s-process path through a ¹⁸⁶Re isomer has been ignored up to now because the neutron capture cross section of the ¹⁸⁵Re(n,γ)^186mRe reaction at a thermal energy as well as a quasi-stellar energy has not been measured by experimental techniques with an estimation of uncertainty. In order to estimate this s-process contamination through the isomer, a production ratio of the isomer to the ground state in ¹⁸⁶Re has been measured through an activation technique with a thermal neutron provided by a nuclear reactor.

The E1 and E2 transition cross sections at the center-of-mass energies of 1.3~1.5MeV have been measured by directly detecting the prompt γ ray from the capture state of the ¹⁶O nucleus. Using a pulsed α beam, major background due to the ¹³C(α,n)¹⁶O reaction were efficiently reduced, and the cross sections were determined with very good statistical accuracy of 4~10%.

Structure of exotic radioactive nuclei having extreme neutron-to-proton ratios is different from that around the stability line. Those nuclei are crucial astrophysically; they pave the highway along which the nuclear material is transported up in the proton and neutron numbers during the complicated synthesis processes in stars. Their structure is also crucial for our understanding of how the stars tick. This short review discusses the progress in microscopic nuclear modeling relevant to nuclear astrophysics.

We review and compare some theoretical models used in nuclear astrophysics: the R-matrix method, the DWBA method, and microscopic cluster models. Applications are presented. The R-matrix theory is illustrated by results of a recent compilation of reactions involved in the Big-Bang nucleosynthesis. The DWBA method is tested with the ¹³C(α,n)¹⁶O reaction, and is shown to be quite sensitive to the conditions of the calculation. Finally, we apply a microscopic model to the ⁷Be(p,γ)⁸B reaction, and update previous results obtained within this framework.

Recently we have performed large-scale calculations of fission barriers in the actinide region based on five-dimensional deformation spaces with more than 3 000 000 deformation points for each potential-energy surface. We have determined new model constants. We have also extended our model to axially asymmetric shapes. We apply these techniques to the calculations of fission barriers of heavy nuclei from the line of beta stability to the r-process line. The aim is to study fission near the end of the r-process. We have also extended our model of β-decay so that allowed Gamow-Teller transitions are treated in a quasi-particle random-phase approximation as earlier, but we now also consider first-forbidden transitions in the statistical gross theory. We discuss the properties of this enhanced model and present results of global calculations.

In RIKEN (The Institute of Physical and Chemical Research) productions and decays of isotopes ²⁷¹110 and ²⁷²111 were studied using a gas-filled recoil ion separator GARIS. The isotopes were produced by ²⁰⁸Pb + ⁶⁴Ni ¤²⁷¹110 + n and ²⁰⁹Bi + ⁶⁴Ni ¤²⁷²111+ n reactions, respectively. Fourteen α-decay chains have been assigned to be the decays originating from the isotope ²⁷¹110. We have observed 14 α-decay chains that can be assigned to subsequent decays from ²⁷²111. The results have provided good confirmations of productions and decays of both the ²⁷¹110 and ²⁷²111 reported by GSI group.

Analysis of ⁸B Coulomb dissociation with the Asymptotic Normalization Coefficient (ANC) method is proposed to determine the astrophysical factor S₁₇(0) accurately. An important advantage of the analysis is that uncertainties of the extracted S₁₇(0) coming from the use of the ANC method can quantitatively be evaluated, in contrast to previous analyses using the Virtual Photon Theory (VPT). Calculation of measured spectra in dissociation experiments is done by means of the method of Continnum-Discretized Coupled-Channels (CDCC). From the analysis of ⁵⁸Ni(⁸B,⁷Be+p)⁵⁸Ni at 25.8 MeV, S₁₇(0) = 22.3 ± 0.64(theo) ± 2.23(expt) (eVb) is obtained; the ANC method turned out to work in this case within 1% of error.

We examine r-process nucleosynthesis in a “prompt supernova explosion” from an 8 - 10M⊙ progenitor star. In the present model, the progenitor star has formed an oxygen-neon-magnesium core at its center. The core-collapse simulations are performed with a one-dimension, Newtonian hydrodynamic code. We simulate energetic prompt explosions by enhancement of the shock-heating energy, in order to investigate conditions necessary for the production of r-process nuclei in such events. The r-process nucleosynthesis is calculated using a nuclear reaction network code including relevant neutron-rich isotopes with reactions among them. The highly neutronized ejecta (Y_e ≈ 0.14 – 0.20) leads to robust production of r-process nuclei; their relative abundances are in excellent agreement with the solar r-process pattern. Our results suggest that prompt explosions of 8 - 10M⊙ stars with oxygen-neon-magnesium cores can be a promising site of r-process nuclei.

We examine the effects of proto-neutron star rotation on r-process nucleosynthesis in the neutrino-driven winds. Finding steady, axisymmetric, rotating wind solutions, we argue the possibility that such a nucleosynthesis effectively takes place there.

We study the effects of neutrino interactions before, during and after the operation of the r-process in a neutrino-driven wind model with a short dynamical timescale. We find that charged- and neutral-current interactions can have specific unique effects on the final abundances. Early on, charged-current interactions determine the electron fraction, while later on, neutrino-induced neutron emission can continue to provide a slight neutron exposure even after the freezeout of the r-process. We propose that observations of an enhanced odd-even effect in the final abundances and a suppression of light nuclei in r-process material might be used to identify the neutrino fluxes in operation near the freezeout of the r-process.

A new accelerator facility RI Beam Factory will be operated in 2006 at RIKEN. Its production capability enables us to study the characteristics of nuclei far from the stability. A new beta counting system has been developed to study the beta decay of rare isotopes produced by fast fragmentation. Our preliminary results on half-life measurement are presented as well as the expected performance of the upgraded system in future.

An experimental program to measure reaction cross sections of (α, n) and (p, n) reactions on light neutron-rich nuclei by using low-energy radioactive nuclear beams is in progress at Tandem accelerator facility of Japan Atomic Energy Research Institute. Exclusive measurements of ⁸Li(α, n)¹¹B and ¹⁶N(α, n)¹⁹F reaction cross sections have been performed successfully. Their excitation functions together with the experimental method are presented.

GRB 030329 has provided solid evidence for the Gamma-Ray Burst -Supernova connection. Spectral observations showed that GRB 030329 is associated with a hypernova, SN 2003dh. We constructed an ejecta model for SN 2003dh by reproducing the spectra. This model is constructed by combining the models for SNe 1998bw and 1997ef. We named this model COMDH. We found that the energetic model, in which Mej = 8M⊙ (M_ms ~ 35 - 40M⊙, E_K = 4 × 10⁵² ergs, and M (⁵⁶Ni) = 0.35M⊙ , is also necessary for light curve fitting.

Recent observational and theoretical advances in studies of gamma-ray bursts (GRBs) indicate that there can be a significant “dark side” to the GRB energy budget: besides the ultrarelativistic jet giving rise to the bright gamma-ray emission, there can be an even greater amount of “dark” energy contained in an accompanying, mildly relativistic outflow. The occurrence of such outflows are strongly supported in theoretical models, particularly for collapsar-type GRB progenitors, and also has been directly confirmed in observations of GRB030329/SN2003dh. This outflow component, which should be more baryon-rich than the GRB jet, can have interesting implications for nucleosynthesis. Inside the outflow, light elements may be produced through reactions similar to big bang nucleosynthesis. Heavy element synthesis by neutron capture can also take place, sometimes by a moderately rapid “n-process” rather than an r-process. The resulting nucleosynthetic products may be observationally relevant for the most metal-poor stars, as well as the companion stars of black hole binary systems.

We investigate nucleosynthesis inside both a gamma-ray burst accretion disk and a wind launched from an inner region of the disk using one-dimensional models of the disk and wind and a nuclear reaction network. Far from a central black hole, the composition of accreting gas is taken to be that of an O-rich layer of a massive star before core collapse. We find that the disk consists of five layers characterized by dominant elements: ¹⁶O, ²⁸Si, ⁵⁴Fe (and ⁵⁶Ni), ⁴He, and nucleons, and the individual layers shift inward with keeping the overall profiles of compositions as the accretion rate decreases. ⁵⁶Ni are abundantly ejected through the wind from the inner region of the disk with the electron fraction ≃ 0.5. In addition to iron group, elements heavier than Cu, in particular ⁶³Cu and ⁶⁴Zn, are massively produced through the wind. Various neutron-rich nuclei can be also produced in the wind from neutron-rich regions of the disk, though the estimated yields have large uncertainties.

The stellar reaction ¹⁴O(α,p)¹⁷F, that critically determines the onset of the high-temperature rp-process, has been studied through a direct measurement with a low-energy radioactive ¹⁴O beam and a gaseous helium target cooled down to 30 K. The reaction cross section was measured by means of a thick target technique in the energy range of E_c.m.(¹⁴O+α) = 0.8-3.8 MeV. The ¹⁴O(α,p)¹⁷F^* reaction leading to the first excited state in ¹⁷F was identified for the first time, suggesting an increase of about 50% for the stellar reaction rate through resonances at around 7.1 MeV in ¹⁸Ne

The ²³Mg+p elastic resonance scattering was observed by using a low-energy radioactive-ion beam of ²³Mg to study resonance levels in ²⁴Al. Resonance patterns were found in the excitation function of the elastic scattering. New information on spin-parities and widths of the ²⁴Al levels may help understand the stellar ²³Mg(p,γ)²⁴Mg reaction rates. Another data of the ²⁴Mg+p resonance scattering, taken simultaneously in the present experiment, confirmed the present experimental technique.

Motivated by the need of spectroscopic data to better understand the astrophysical rp-process, we developed a new experimental method using the Grand Raiden magnet spectrometer to study proton rich nuclei with α and ³He induced reactions. The results of the ²⁴Mg(⁴He,⁶He)²²Mg reaction at 205 MeV and 0° are presented, showing states relevant for resonant reaction rate calculations of the proton capture ²¹Na(p,γ)²²Mg and ¹⁸Ne(α,p)²¹Na reaction which controls the break-out of the hot CNO cycles at X-ray burst conditions. In addition, the results of the ²⁸Si(⁴He,⁶He)²⁶Si reaction are presented, showing states relevant to the production rate of ²⁶Al in its ground state which provides models of the explosive hydrogen burning process in novae and supernovae.

The long-lived radioactive nuclide ²²Na (t_1/2 = 2.6 y) is, in principle, an astronomical observable for understanding the physics processes of oxygen-neon novae. Production and abundance yields of ²²Na in these events are dependent to the hitherto unknown rate of the ²¹Na(p,γ)²²Mg reaction. Using a high intensity radioactive ²¹Na beam at the TRIUMF-ISAC facility, direct measurements of the strengths of six potentially astrophysically important resonances have been made at center of mass energies in the range: E_cm = 200 to 850 keV. Reported herein are preliminary results obtained for these strengths and their respective contributions to the ²¹Na(p,γ)²²Mg stellar reaction rate.

We investigate the properties of the neutron star matter with the relativistic mean field models. We incorporate in quantum hadrodynamics and quark-meson coupling models a possible reduction of meson masses in nuclear matter. The equation of state for neutron star matter is calculated at the matter densities up to 4 times the nuclear saturation density. We find that the equation of state and the composition of the matter are sensitive to the behavior of meson masses in medium.

Possibility of the structured mixed phases at first order phase transitions in neutron stars is reexamined by taking into account the charge screening effect. The Maxwell construction is shown to be not conflicted with the Gibbs conditions once the Coulomb potential is properly taken into account. Taking the hadron-quark deconfinement transition as an example, we explicitly demonstrate a mechanical instability of the geometrical structure of the structured mixed phase by the charge screening effect. In this case we have effectively the picture given by the Maxwell construction.

The equation of state (EOS) of asymmetric nuclear matter dominates macroscopic properties of neutron rich nuclei in laboratories, and extremely neutron-rich pasta nuclei (rodlike and slablike nuclei and rodlike and spherical nuclear bubbles) in a neutron star crust. The purpose of this study is to identify the most important EOS parameter that governs the radii of neutron-rich laboratory nuclei and the density range of the pasta nuclei. In a simplified Thomas-Fermi method, we calculate the masses and density distributions of neutron-rich laboratory nuclei and pasta nuclei using various EOS’s that are consistent with empirical data for masses and radii of stable nuclei, and systematically examine the EOS dependence of the matter radii of laboratory nuclei and the density range of the crustal part including pasta nuclei. It is found that both the calculated matter radii of neutron-rich laboratory nuclei and the calculated density range of the pasta nuclei show a clear dependence on the density symmetry coefficient L, while the dependence on the incompressibility K₀ is much weaker. The density range of the pasta nuclei is found to disappear for extremely large L values. These results suggest that future systematic measurements of the matter radii of neutron-rich nuclei could help deduce the L value, which in turn could give useful information about the presence of pasta nuclei in neutron star crusts.

Using the density functional theory (DFT) with the relativistic mean field (RMF) model, we study the non-uniform state of nuclear matter, “nuclear pasta”. We self-consistently include the Coulomb interaction together with other interactions. It is found that the Coulomb screening effect is significant for each pasta structure but not for the bulk equation of state (EOS) of the nuclear pasta phase.

Measurements of isotope abundances give quite strong constraints on nucleosynthesis models. High resolution spectrographs recently mounted on large telescopes enable us to measure isotope abundances for several elements in metal-deficient stars. We report on the measurements of isotope abundances for Europium and Lithium using the 8.2m Subaru Telescope.

We present the abundance analyses for the neutron-capture elements in very metal-poor stars based on the high-quality spectra obtained with the Subaru Telescope High Dispersion Spectrograph. Our study covers elements from light neutron-capture nuclei to the heaviest ones. The abundance patterns of elements around Ba and Eu are quite similar to that of the r-process component in solar-system material, suggesting the origin of neutron-capture elements is r-process in these metal-poor stars. However, the abundance ratios between Sr and Ba show a very large scatter. Th/Eu ratios also show a scatter, even though that is much smaller than the scatter found in Sr/Ba. These results provide a quite useful constraints on r-process modeling and will be useful to search for the sites of this process.

Recent observations of extremely metal-poor stars suggest that the primary spallation process dominated the light element (Li,Be,B) nucleosynthesis in the early galaxy. To investigate the energy spectra of SN ejecta which mainly consist of C/O, we have performed numerical calculations of type Ic supernova explosions using a relativistic hydrodynamic code with realistic numerical models for massive stars and a realistic equation of states. Moreover, we estimate the yields of light elements by spallation reactions using the energy spectra from our numerical calculations together with empirical cross sections of the reactions. We find that the adiabatic index becomes larger than 4/3 in a mild explosion and the acceleration of ejecta becomes more efficient. We also find that not only highly energetic explosions like SN 1998bw but also normal Ic SNe explosions significantly accelerate their outermost layers beyond the threshold energy of spallation reactions. On the other hand, the accelerated ejecta lose their energy because of interactions with the interstellar neutral atoms before they undergo spallations with the interstellar H and/or He. Though the abundance ratios such as Li/Be and Be/B are compatible with observations, none of type Ic supernovae (SNe Ic) could be main sources of light elements in the Galactic halo, as long as most of the interstellar atoms are not ionized. If 99 % of the interstellar H are ionized, SNe Ic like SN 2002ap can be candidates of light element sources.

The influence of the neutrino luminosity on the nucleosynthesis of the light elements ⁷Li and ¹¹B and the r-process heavy elements in Type II Supernovae is investigated. Common models of the neutrino luminosity, which are parameterized by the total energy E_ν and decay time τ_ν, are adopted to understand both processes. The supernova explosion of a 16.2 M⊙ star, which corresponds to SN 1987A, is calculated and the light element synthesis is pursued by postprocessing. The ejected masses of ⁷Li and ¹¹B are roughly proportional to E_ν but are insensitive to τ_ν. As for the r-process, the same models of neutrino luminosity are adopted in the neutrino-driven wind models of a 1.4 ⊙ neutron star. The r-process is affected through the peak neutrino luminosity, which relates to E_ν/τ_ν. An unsolved problem of the overproduction of ¹¹B in the galactic chemical evolution is discussed. The total neutrino energy should be smaller than 1.2 × 10⁵³ ergs to avoid the overproduction of ¹¹B, which is too small to accept compared to 3.0 × 10⁵³ ergs deduced from the observation of SN 1987A. We here propose to reduce the temperature of ν_μ,τ and to 6.0 MeV/k in a model with E_ν ~ 3 × 10⁵³ ergs and τ_ν = 9.0 s. This modification is shown to resolve the overproduction problem of ¹¹B while still preserving a successful r-process abundance pattern.

We studied Mg isotope ratios in globular-cluster stars using a simple supernova-induced self-enrichment model. Our basic idea is to explain the observed Mg isotope ratios by the contribution from an early generation of intermediate-mass stars. Although our model produces some Mg isotopic abundance variation, not enough heavier Mg isotopes (²⁵Mg and ²⁶Mg) were formed unless star formation occurs in low density regions behind the super shell. In our model, the 1st generation of AGB stars could not affect heavier Mg isotopes if we assume contamination occurs in the super shell. We also discuss neutron-capture elements in M15 using the same model. It appears difficult to explain current observational results by cloud-collision models. If we assume the r-process occurs in low-mass supernovae, (e.g., ONeMg supernovae), our self-enrichment model can reproduce the observed [Ba/Fe] scatter.

We have performed a Coulomb dissociation experiment of ²³Al to study the stellar ²²Mg(p,γ)²³ Al reaction. The radiative width of the first excited state in ²³Al, which can affect the resonant reaction rate, is determined experimentally for the first time.

Resonant states in ²³Al related to the astrophysical ²²Mg(p, γ) reaction, were firstly investigated by using the resonant elastic scattering of ²²Mg+p with a low-energy radioactive-ion beam of ²²Mg at 4.38 MeV/nucleon and a thick (CH₂)_n target. A new resonant state at 2.99-MeV was observed in the spectrum of recoil protons.

Preliminary LTE and non-LTE (NLTE) analyses of oxygen (O) abundances were carried out for the 19 metal-poor stars and the two normal stars, Procyon and the Sun, based on high-resolution, high-signal-to-noise spectra obtained with OAO/HIDES as well as on the ELODIE spectral database. The forbidden lines [O I] 6300/6363 Å were analyzed on LTE assumption, while the triplet lines O I 7772-5 Å were corrected for NLTE effects. Our main results are: (1) NLTE [O/Fe] derived from the triplet lines distribute almost flat with an average of ~ 0.75 dex in the range of [Fe/H]< −1, while those from the forbidden lines seem to show an increasing trend with decreasing [Fe/H], which must be confirmed by a further detailed study. (2) The triplet-line NLTE [O/Fe] are systematically larger than the forbidden-line [O/Fe] by an average of ~ 0.35 dex in the range of −2 <[Fe/H]< 0.

In the framework of RMF containing the full baryon octet [1] , we have made the EOS table at high densities combined with the relativistic nuclear EOS table [2] at lower densities. Both parts of the table is based on the TM1 parameter [3] of RMF, then the table covers wide range of nuclear densities, from 10^5.1g/cc to 10^15.4g/cc, smoothly. As a sample calculation by using this new EOS table, we perform 1-dim. spherical hydrodynamical calculation [4] with the relativistic EOS of supernova matter including hyperons and discuss the EOS dependence of the explosion energy. For the most attractive Σ potential case, we find that hyperons increase the explosion energy by about 4 % in the case of 15M_o model. We also show the element composition around core bounce, where ρ ~ 1.6p. At this density, hyperons can appear due to finite temperature effects. Although the hyperon ratio is small, it leads to the reduction of pressure by around 3 %. In this paper, we discuss the mechanism of hyperon admixture, and progenitor mass dependence on hyperon ratio.

We present results of p-process nucleosynthesis in core collapse supernovae (SNe). We focus on the influence of different explosion energies and metallicities on p-process yields. We find that overproduction factors have a strong sensitivity on peak temperatures and that the distribution of normalized mean overproduction factors is robust to changing the explosion energy and metallicity. Our results indicate that (1) the contribution to the galactic evolution of p-nuclei from stars with Z ≲ Z⊙/20 reduces significantly, and (2) more massive (M ≳ 25M⊙) and energetic SNe may be a dominant production site of the p-nuclei.

Ultra-relativistic nucleus-nucleus collisions create a state of matter of high temperature and small baryo-chemical potential, which is similar to the thermodynamical conditions in the primordial universe. Recent analyses of Au+Au collisions at RHIC revealed the temperature, size and density of the system. Thus, a comparison to the primordial universe can be attempted. In particular, two observables shall be investigated, namely (1) the temperature at baryon freeze-out (t≃10 fm/c in the Au+Au collision) and (2) the matter density at the partonic stage (t≤1 fm/c).

Non-uniform structures of the mixed phase during the first-order kaon condensation, using the density functional theory with the relativistic mean-field model. Including the Coulomb potential and applying the Gibbs conditions in a proper way, we numerically determine the density profiles of nucleons, electrons and condensed kaons The importance of the Coulomb screening effects is elucidated and thereby we suggest that the Maxwell construction is effectively justified.

The observational space map of 1.809-MeV gamma rays - coming from the decay of ²⁶Al - taken by COMPTEL requires the sources and their nucleosynthetic activity to be unveiled. One suggestion for the observation is the explosive hydrogen burning process which occurs in novae or X-ray bursts. Two capture reactions such as ²⁵ Al(p,γ)²⁶Si and ²⁶Si(p,γ)²⁷P are of great importance in the production of 1.809-MeV gamma rays. Resonance states within the Gamow window should be precisely known to determine their reaction rates. As for the latter reaction, only a few levels in ²⁷P have been known above the proton threshold in comparison with many levels known in its mirror nucleus ²⁷Mg. We studied proton resonances in ²⁶Si and ²⁷P by the elastic scattering at low energies, respectively using low-energy ²⁵Al and ²⁶Si radioactive ion beams available from the CRIB facility at CNS, University of Tokyo. We carried out an experiment to investigate proton resonances in ²⁶Si up to E_C.M. = 3.016 MeV, especially to determine the resonance parameters of the states at E_x = 7.019 and 8.120 MeV. We also measured the elastic scattering of p + ²⁶Si up to E_C.M. = 3.290 MeV.

We have investigated the formation of dust grains in the ejecta of Population III supernova; core collapse supernovae with the progenitor mass M_pr ranging from 13 to 30 M⊙ and pair-instability supernovae with M_pr = 170 and 200 M⊙. In this paper, we report the amount of dust grains formed in the ejecta of Population III supernovae, and discuss the time evolution of dust-to-gas mass ratio and metallicity in the primordial universe.

The behaviour of the quasi-free p-p elastic cross section was investigated by using the Trojan Horse Method and the ²H(p,pp)n reaction. This reaction has been recently studied at Laboratori Nazionali del Sud, INFN, Catania at a proton beam energy of 6 MeV. The extracted two-body cross section is compared with the free pp one at relative enegies where the free p-p cross section is sensitive to the Coulomb interaction.

Very massive stars ≥ 8M⊙ culminate their evolution by supernova (SN) explosions which are presumed to be most viable candidate for the astrophysical site of heavy r-process nucleosynthesis. In an explosive circumstances of the neutrino-driven winds in gravitational core-collapse Type II SNe, not only heavy neutron-rich nuclei but also light unstable nuclei play the significant roles. We first studied in this article the efficiency and sensitivity of the SN r-process nucleosynthesis to many relevant nuclear reaction rates. Our adopted theoretical method and formulae are very effective, and their successful power has already been established in theoretical studies of the missing solar neutrino problem. We also adopted two different models of the neutrino-driven winds in order to study the dependence of our result on wind models. In this study we found quantitatively that several specific nuclear reactions on light neutron-rich nuclei take very critical keys to the final nucleosynthesis yields of r-process elements [1]. Our numerical result of the sensitivity analysis emphasizes and motivates the importance of future experiments aimed at unambiguously determining the nuclear reaction rates that most strongly affect the SN r-process abundance. It would in turn serve to constrain physical and environmental conditions for successful r-process nucleosynthesis in exploding Type II SNe.

We should clarify several problems for the Re-Os pair to be used as one of the good cosmochronometers. First, since ¹⁸⁷Os is formed and depleted by sequential neutron capture in stars, the effects should be corrected. Second, ¹⁸⁷Os is depleted by the neutron capture process through the excited state at 10keV. It is very important to find a proper way to correct for the s-process contribution in deducing the age of the Galaxy. In order to correct for the effect mentioned above and to determine the age of the universe, we are planning to measure the neutron capture cross section of the first excited state (E_excited = 10 keV) of ¹⁸⁷Os is one of the key parameters in deduceing the age of the Galaxy using the Re-Os cosmochronometer. In order to deduce the cross section we are preparing various detectors using a newly developed experimental method. In these paper I briefly describe our experimental methods to accurately determine the neutron caprute cross section of the first excited state of ¹⁸⁷Os.

Recent measurements with radioactive beams at ORNL’s Holifield Radioactive Ion Beam Facility (HRIBF) have prompted the evaluation of a number of reactions involving unstable nuclei needed for stellar explosion studies. We discuss these evaluations, as well as the development of a new computational infrastructure to enable the rapid incorporation of the latest nuclear physics results in astrophysics models. This infrastructure includes programs that simplify the generation of reaction rates, manage rate databases, and visualize reaction rates, all hosted at a new website www.nucastrodata.org.

No abstract received.

To study double spin-isospin responses in view of the ββν decays, double charge-exchange nuclear reactions have measured at RCNP. We have succeeded to measure the double charge exchange reaction by means of heavy ion reaction. From these experiments, we conclude that the (¹¹B,¹¹Li) reaction at 70 MeV/nucleon is a good spectroscopic tool. We believe that the reaction can be well applied to the study of pure spin-flip nuclear responses in higher-excited regions including DGT and higher ∆L excitations.

Measuring the distribution of nuclear recoil angles is said to be one of the most reliable methods to identify a positive sign of weakly interacting massive particles (WIMPs) which are leading candidates for the cold dark matter. We evaluated the detection feasibility with CF₄ gas for spin-dependent (SD) interactions and Xe gas for spin-independent (SI) interactions taking into account the performance of the µ-TPC which is an existing three-dimensional tracking detector. We consequently found that the µ-TPC filled with CF₄ gas can reach the best sensitivity of the current experiments for SD interactions with even. a 0.3m³ · year of exposure at Kamioka Observatory (2700 m.w.e.). We also found it is possible to explore the theory regions predicted by minimal supersymmetric extensions of the standard model (MSSM) via SD and SI interactions with a sufficient exposure (~ 300m³ · year).

We investigate important reactions and reaction paths in order to reproduce the isotopic ratios of characteristic elements, C, N, and Si, in presolar SiC grains from novae. We find that the N-isotopic ratio strongly depends on the temperature profile in a nova explosion. By using this temperature dependence, we obtain a favorable temperature profile during a nova outburst. Moreover, the calculated ³⁰Si/²⁸Si ratio is high compared with the observational data of presolar nova grains. We also find that this overproduction of ³⁰Si can be avoided if the reaction rate of ³⁰P(p,γ)³¹S, which is experimentally still unknown, could increase by a factor of a few tens around the temperature of ~3 × 10⁸ K.

The ground state properties of the carbon isotopes are investigated using the extended version of the Antisymmetrized Molecular Dynamics (AMD) Multi Slater Determinant method. We can reproduce reasonably well many experimental data for ¹²C-²²C. In this contribution we present a systematic calculation of binding energies, energies of the 2¹₊ states and B(E2) transition strengths.

The Coulomb dissociation of ²⁷P was studied experimentally using ²⁷P beams at 57 MeV/nucleon with a lead target. The gamma decay width of the first excited state in ²⁷P was extracted for astrophysical interest. A preliminary result is consistent with the value estimated on the basis of a shell model calculation by Caggiano et al.

The ⁷Li(p,α)⁴He ⁶Li(d,α)⁴He and ⁶Li(p,α)³He reactions was performed and studied in the framework of the Trojan Horse Method applied to the d(⁷Li,αα)n, ⁶Li(⁶Li,αα)⁴He and d(⁶Li,α³He)n three-body reactions respectively. Their bare astrophysical S-factors were extracted and from the comparison with the behavior of the screened direct data, an independent estimate of the screening potential was obtained.

Neutron skin thickness of stable and unstable nuclei are studied by using Skyrme Hartree-Fock (SHF) models and relativistic mean field (RMF) models in relation with the pressure of EOS in neutron matter. We found a clear linear correlation between the neutron skin sizes in heavy nuclei, ¹³²Sn and ²⁰⁸Pb and the pressure of neutron matter in both SHF and RMF, while the correlation is weak in unstable nuclei ³²Mg and ⁴⁴Ar.

How many isotopic ratios of individual presolar grains from supernovae agree with those of the mixtures of Type II supernova ejecta with appropriate mixing ratios is investigated. Detailed nucleosynthesis during the evolution and supernova explosion of a 4 M⊙ He star is calculated by postprocessing. Using the obtained supernova ejecta, two cases of mixtures are considered with artificial mixing ratios: one consists of the Si/S, O/Ne, He/C, and He/N layers and the other consists of the Ni, Si/S, He/C, and He/N layers. The isotopic ratios of ¹²C/¹³C, ¹⁴N/¹⁵N, ²⁶Al/²⁷Al, ²⁹Si/²⁸Si, ³⁰Si/²⁸Si, and ⁴⁴Ti/⁴⁸Ti are chosen from eleven SiC grains and four low density graphite ones which contain evidence for the original presence of the short-lived isotope ⁴⁴Ti. For one SiC X grain and one low density graphite grain, four isotopic ratios are reproduced by the corresponding mixtures. For ten SiC X and low density graphite grains, three isotopic ratios of the grains agree with those of the mixtures. Most of the mixtures reproducing the isotopic ratios of the grains are rich in the composition of the He/N layer. The characteristics of the mixtures are found to be 0.1 < Si/C < 1 and Ti/C < 0.1.

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