Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session CF: Nuclear Astrophysics I |
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Sponsoring Units: DNP JPS Chair: Taka Kajino, NAO-Japan Room: Ritz-Carlton Hotel Plantation 3 |
Tuesday, September 20, 2005 2:00PM - 2:15PM |
CF.00001: S-factors of capture reactions important for astrophysics from {\it ab initio} wave functions Petr Navratil, Christian Forssen, Erich Ormand, Carlos Bertulani, Etienne Caurier Nuclear structure of $^3$He, $^4$He, $^7$Be, $^8$B, $^{10}$Be and $^{11}$Be is studied within the {\it ab initio} no-core shell model (NCSM). Starting from realistic inter-nucleon interactions, wave functions for these nuclei are obtained in basis spaces up to $12\hbar\Omega$ and then used to calculate cluster form factors (overlap functions) for the bound states of $^8$B with $^7$Be+p, $^7$Be with $^3$He$+^4$He and $^{11}$Be with $^{10}$Be+n as a function of the separation between the two interacting clusters. Due to the use of the harmonic oscillator basis, the overlap functions have incorrect asymptotics. To fix this problem, we perform a least-square fit of Woods-Saxon potential solutions to the NCSM overlap functions in the range from 0 fm up to about 4 fm under the constraint that the experimental separation energy is reproduced. The corrected overlap functions are then used for the $^7$Be(p,$\gamma$)$^8$B, $^3$He($\alpha$,$\gamma$)$^7$Be and $^{10}$Be(n,$\gamma$)$^{11}$Be S-factor calculations. Support from the LDRD contract No. 04-ERD-058 as well as partial support from the DOE grants SCW0498 and DE-FG02-04ER41338 is acknowledged. [Preview Abstract] |
Tuesday, September 20, 2005 2:15PM - 2:30PM |
CF.00002: Study of the $^{10}\mathrm{Be}(n,\gamma)^{11}\mathrm{Be}$ reaction and strong E1 transitions in $^{11}$Be using \emph{ab initio} wave functions Christian Forssen, Petr Navratil, Erich Ormand, Etienne Caurier We present calculations of $^{10}\mathrm{Be}(n,\gamma)^{11}\mathrm{Be}$ which is a possible breakthrough reaction in the primordial nucleosynthesis of inhomogeneous Big Bang scenarios. We employ \emph{ab initio} nuclear structure information from a recent study performed in the framework of the no-core shell model (NCSM). Cluster form factors are extracted from the NCSM wave functions and corrected to reproduce the known asymptotics. These overlaps are then used in two-body potential model calculations of the capture reaction and we find a large contribution from direct $p$-wave capture which has important consequences for the predicted reaction rate. Our corrected cluster form factors can also be used to compute the extraordinarily strong E1 transition between the two bound states in $^{11}$Be under the approximation that it is a pure single-particle transition. We find a significant improvement compared with our previous result that was obtained with NCSM $A$-body wave functions expanded in the harmonic oscillator basis. Support from the LDRD contract No. 04-ERD-058, and from U.S. Department of Energy, Office of Science, (Work Proposal Number SCW0498) is acknowledged. [Preview Abstract] |
Tuesday, September 20, 2005 2:30PM - 2:45PM |
CF.00003: New Approach to M1 Cross Section for D(gamma,n) via the D(7Li,7Be) Reaction. S. Nakayama, T. Yamagata, H. Akimune, Y. Arimoto, I. Daito, H. Ejiri, H. Fujimura, Y. Fujita, M. Fujiwara, K. Fushimi, M.B. Greenfield, H. Kohri, N. Koori, K. Takahisa, T. Takeuchi, M. Tanaka, K. Yonehara, H.P. Yoshida The n-p capture cross section is inferred via the ``detailed balance'' of the deuteron photodisintegration by using the gamma-d cross section above the deuteron binding energy of Ex=2.225 MeV up to and including the energy region in the Big Bang (BB). In the threshold energy region, the contribution of the M1 capture process dominates over the E1 capture process. The gamma-d cross sections in the threshold energy region can then provide parameters used in evaluations of nucleosynthesis in the early universe. In this contribution we present a new method to deduce the M1 gamma-d cross section as a function of excitation energy in the deuteron by using the charge-exchange spin-flip (CESF) reaction. The CESF reaction of (7Li,7Be) at 65 A MeV was used to deduce the distribution of the B(M1) reduced matrix elements for the photodisintegration of the deuteron from the analogous B(GT) distribution. The results are in agreement with recent photodisintegration measurements and effective field calculations. [Preview Abstract] |
Tuesday, September 20, 2005 2:45PM - 3:00PM |
CF.00004: Neutrino-nucleus reactions in a supernova environment Futoshi Minato, Kouichi Hagino, Noboru Takigawa, A. Baha Balantekin There is a suggestion that the neutrino induced fission in the supernova environment may alter the r-process pattern for the element abundance. In order to assess the role of temperature in the neutrino induced fisson, we perform thermal RPA calculations for neutrino-nucleus interactions. Advantages of this method are that it can be easily applied to heavy nuclei and that excitations to the continuum states can be included exactly. We will systematically discuss how the temperature affects the reaction rate, and its implication for the neutrino induced fission. [Preview Abstract] |
Tuesday, September 20, 2005 3:00PM - 3:15PM |
CF.00005: Shock propagation in prompt supernova explosion and the MSW effect of neutrino Shiou Kawagoe, Toshitaka Kajino, Kazuhisa Yoshihara, Hideyuki Suzuki, Kohsuke Sumiyoshi, Shoichi Yamada The MSW effect of supernova neutrino is the focus of recent neutrino astrophysics. It is still an open question how the shock wave propagation affects the neutrino oscillation. Using an implicit Lagrangian code for general relativistic spherical hydrodynamics, we succeeded in numerical simulations of breakout of shock wave propagation through the stellar envelope. We first discuss our successful result of shock wave propagation which is generated by adiabatic collapse of iron core and compare with non-adiabatic collapse. Secondly, we apply this model to the neutrino oscillation and calculate survival probabilities of three light-neutrino families. We discuss how the flux and energy spectrum of each neutrino species can change due to the MSW effect. [Preview Abstract] |
Tuesday, September 20, 2005 3:15PM - 3:30PM |
CF.00006: Active-Sterile Neutrino Transformation: Consequences for Supernova Nucleosynthesis Joshua Beun, Rebecca Surman, Gail McLaughlin, William Hix We consider a fourth, sterile neutrino and study the implications for core collapse supernovae. In particular, we consider the effect of such an additional neutrino on the nucleosynthesis which occurs in the neutrino driven wind. We present calculations of neutrino flavor transformation coupled to a nuclear reaction network. We comment on the prospects for obtaining the r-process elements in this scenario. [Preview Abstract] |
Tuesday, September 20, 2005 3:30PM - 3:45PM |
CF.00007: General Relativistic Instability in Supermassive Objects: Neutrinos and Nuclear Physics Chad Kishimoto, George Fuller We discuss the general relativistic instability in very high mass stellar objects. The high entropy electron-positron plasma in these stars serves as an engine for efficient production of neutrinos and antineutrinos of all flavors, with $\sim 5\%$ of the rest mass of the star converted to neutrinos during its collapse to a black hole. We examine the influence of these prodigious neutrino and antineutrino fluxes on the evolution of the nuclear component in these objects. [Preview Abstract] |
Tuesday, September 20, 2005 3:45PM - 4:00PM |
CF.00008: Two-Dimensional Simulations of Core-Collapse Supernovae: The Role of Anisotropic Neutrino Radiation Hideki Madokoro We have carried out two-dimensional numerical simulations of core-collapse supernovae. Special attention was paid to the role of anisotropic neutrino radiation on the explosion dynamics. It was revealed (Shimizu et al. 2001, Astrophys. J. 552, 756; Madokoro et al. 2003, Astrophys. J. 592,1035; Madokoro et al. 2004, Publ. Astron. Soc. Japan 56, 663) that a small amount of anisotropy in the neutrino flux can increase explosion energies to a large extent when total neutrino luminosity was fixed and the profile of the neutrino flux was assumed. In the previous talk, we showed our first results starting from the onset of core-collapse. It was confirmed that collapse, bounce and shock formation were correctly reproduced in our simulations. Neutrino heating and cooling were, however, omitted due to difficulty of treating neutrino transport in multi-dimensional calculations. In this talk, our new results are shown in which the effects of neutrino heating and cooling are approximately included. Especially we will discuss the origin of anisotropic neutrino radiation, the degree of anisotropy, and the effects of anisotropic neutrino emission on the explosion mechanism. [Preview Abstract] |
Tuesday, September 20, 2005 4:00PM - 4:15PM |
CF.00009: Phase diagrams of nuclear ``pasta'' invetigated by QMD simulation Hidetaka Sonoda, Gentaro Watanabe, Katsuhiko Sato, Kenji Yasuoka, Toshikazu Ebisuzaki At subnuclear densities, such as in the inner crust of neutron stars and in the core of supernovae, it is pointed out that nuclei can adopt nonspherical shapes like rods or plates due to competition between the Coulomb energy and the nuclear surface energy. These nonspherical nuclei are referred to as nuclear ``pasta.'' We are studying these exotic phases by using Quantum Molecular Dynamics (QMD), which is a dynamical method and does not impose any assumptions on shapes of nuclei. Previous works investigated phase diagrams of nuclear matter at subnuclear densities by using a certain phenomenological QMD model Hamiltonian. But phase diagrams are influenced by various nuclear parameters such as surface energy, incompressibility, and properties of pure neutron matter. We noticed uncertainties of these nuclear parameters are essential and studied phase diagrams of nuclear pasta in the ranges of these uncertainties by QMD simulation. [Preview Abstract] |
Tuesday, September 20, 2005 4:15PM - 4:30PM |
CF.00010: Properties of Nuclear and Neutron Matter in the Nonlinear $\sigma$-$\omega$-$\rho$ Dirac-Hartree-Fock Approximation Hiroshi Uechi \newcommand{\bkappa}{\mbox{\boldmath $\kappa$}} \newcommand\kfermi{k_{\scriptscriptstyle F}} \newcommand\Mstar{M^{\ast}} \newcommand\kstar{k^{\ast}} \newcommand\rhoB{\rho_{\scriptscriptstyle B}} \newcommand\szero{\scriptscriptstyle (0)} \newcommand{\bftau}{\mbox{\boldmath $\tau$}} A self-consistent relativistic Dirac-Hartree-Fock (DHF) approximation in a nonlinear $\sigma$-$\omega$-$\rho$ mean-field model is discussed by employing conditions of the theory of conserving approximations. The approximation is applied to Fermi-liquid properties of nuclear matter and properties of neutron stars in order to produce the effective mass of nucleon, $M^{\ast}/M \sim 0.7$, incompressibility $ \sim 250$ MeV, symmetry energy $a_4 \sim 30$ MeV, the maximum mass of neutron star $M_{star}/M_{\odot} = 2.5$, by adjusting coupling constants of nonlinear interactions. The results of nonlinear $\sigma$-$\omega$-$\rho$ Hartree approximation (NHA) and the linear Hartree ($\sigma$-$\omega$) approximation (LHA) are listed in the table. % \vspace{-0.5cm} \begin{center} \arrayrulewidth=1.0pt \doublerulesep=0pt \begin{tabular}{lcccccc} \\ \hline\hline & $M^{\ast}/M$ & $m_{\sigma}^{\ast}/m_{\sigma}$ & $m_{\omega}^{\ast}/m_{\omega}$ & $K$ (MeV) & $a_4$ (MeV) &$M_{max}$ \\ \hline\hline LHA & 0.54 & 1.00 & 1.00 & 530 & 19.3 & 3.03 \\ NHA & 0.68 & 1.09 & 1.05 & 303 & 25.7 & 2.50 \\ \hline\hline \end{tabular} \end{center} Since nonlinear self-interactions of mesons are renormalized as effective masses of mesons by self-consistency and strictly restricted by coupled equations of motion for mesons and baryons, the validity of nonlinear self-interactions of mesons would be examined by analyzing nuclear experimental data and properties of neutron stars. [Preview Abstract] |
Tuesday, September 20, 2005 4:30PM - 4:45PM |
CF.00011: Two-body Weak Interactions Using Correlated Basis Theory Shannon Cowell, Joseph Carlson In the last several decades it has become clear that neutrino interactions play an important role in many astrophysical environments from the dynamics of core-collapse supernovae to the cooling of neutron stars. Simulations of such processes require an accurate description of neutrino interactions with nucleon matter at a variety of temperatures, proton fractions and densities. Many previous calculations of the relevant neutrino cross sections are inconsistent, using empirical effective interactions together with bare weak operators. We address this inconsistency using correlated basis theory (CBT) which allows for a systematic definition of both effective interactions and effective weak operators. Previous CBT calculations of the one-body weak processes relevant in core collapse supernova have shown that short range correlations are important in both the effective interactions and operators. For example, neutrino mean free paths calculated using CBT and TDA are a factor of 2-4 larger than the simple non-interacting Fermi gas. In this talk, we will discuss the CBT two-body weak operators relevant for the highly asymmetric matter of neutron stars. [Preview Abstract] |
Tuesday, September 20, 2005 4:45PM - 5:00PM |
CF.00012: Influence of Interstellar Neutrals as an Atmosphere on Charged Particle Flux in the Heliosphere M.A.K. Lodhi, Thomas Wilson, Abel Diaz It has been shown that the charged particle flux in the Earth's trapped radiation belts is a bi-variant function of energy and atmospheric density [1,2], where the density is modulated by variation in activity of the Sun during its solar cycle. This result was derived from a regression algorithm technique used in nuclear physics for studying momentum-dependent potentials. A dynamic background of atmospheric neutrals, then, has a definite effect upon charged-particle flux and fluence and contributes to energy losses primarily due to multiple neutral and Coulomb scattering. Cosmic-ray flux is not merely a function of energy, but rather is a two-dimensional surface depending upon density of atmospheric neutrals as well. We extend this result to the Sun's heliosphere where the source of atmospheric neutrals is the Local Interstellar Medium (LISM) of the Galaxy. The Sun's activity once again modulates density in the heliosphere via the solar wind's heliopause, while inhomogeneities in the LISM affect the neutral density as the heliosphere moves through it. As to be expected, the low-energy cosmic-ray flux is bi-variant in energy and density of neutrals. Anomalous cosmic rays naturally participate in this picture. [1] Lodhi, M.A.K., et al., \textit{Rad. Meas.} 39, 391 (2005). [2] Diaz, A., et al., \textit{Lunar and Planetary Sci. }36, 1197 (2005). [Preview Abstract] |
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