Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session HF: Topics In Nuclear Theory |
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Sponsoring Units: DNP Chair: David Ernst, Vanderbilt University Room: Gaylord Opryland Hermitage C |
Saturday, October 28, 2006 2:00PM - 2:12PM |
HF.00001: Neutron-Proton Bremsstrahlung Compared to Experiment at 225 MeV Virginia Brown, Jerrold Franklin, Perry Anthony Neutron-proton bremsstrahlung ($np\gamma$) with out-of-plane contributions, relativistic spin effects, charge form-factor contributions, and meson-exchange effects included to order K in the photon momentum [1] are calculated with various modern nucleon-nucleon potentials to compare to experimental results at 225 MeV obtained by J. Matthews et al.[2] at LANCE. The data include various coplanar nucleon exit angles. These are the first experimental ($np\gamma$) data to explicitly measure the photon angular distribution. Finite-size detector effects are determined with the out-of-plane calculations. \newline \newline [1] V. R. Brown and J. Franklin, Phys. Rev. C {\bf 8}, 1706 (1973). \newline [2] J. Matthews and T. Akdogan, private communication. [Preview Abstract] |
Saturday, October 28, 2006 2:12PM - 2:24PM |
HF.00002: How to Classify Three-Body Forces -- and Why Harald W. Griesshammer \newline To add 3-body forces when theory and data disagree is untenable when predictions are required. For the ``pion-less'' Effective Field Theory at momenta below the pion-mass, I provide a recipe to systematically estimate the typical size of 3-body forces in all partial waves and orders, including external currents~[1]. It is based on the superficial degree of divergence of the 3-body diagrams which contain only two-body forces and the renormalisation-group argument that low-energy observables must be insensitive to details of short-distance dynamics. Na\"ive dimensional analysis must be amended as the asymptotic solution to the leading-order problem depends for large off-shell momenta crucially on the partial wave and spin-combination considered. The typical strength of most 3-body forces turns out weaker than expected, demoting many to high orders. As application, the cross section of $nd\to t\gamma$ at thermal neutron energies bears no new 3-body force~[2], besides those fixed by the triton binding energy and $nd$ scattering length in the triton channel. It is calculated as $[0.485(\mathrm{LO})+0.011(\mathrm{NLO})+0.007(\mathrm{NNLO}) ]\;\mathrm{mb}=[0.503\pm0.003]\;\mathrm{mb}$, converges and compares well with experiment, $[0.509\pm0.015]\;\mathrm{mb}$. In contradistinction, potential models list a spread of $[0.49\dots0.66]\;\mathrm{mb}$, depending on the 2-nucleon potential and inclusion of the $\Delta(1232)$. \newline [1] H.W.~Grie{\ss}hammer: Nucl.~Phys.~\textbf{A760} (2005) 110 [2] H.~Sadeghi, S.~Bayegan and H.W.~Grie{\ss}hammer, in preparation. [Preview Abstract] |
Saturday, October 28, 2006 2:24PM - 2:36PM |
HF.00003: Realistic three-nucleon effective interaction from the folded-diagram theory Maxim Kartamyshev, Morten Hjorth-Jensen, Torgeir Engeland, Eivind Osnes Starting from the folded-diagram theory of Kuo and collaborators, we construct an effective three-nucleon interaction originating from the two-nucleon force. Influence of the three-nucleon terms on nuclear properties is investigated in shell-model studies of selected nuclei in $^{16}$O, $^{40}$Ca and $^{100}$Sn mass regions. [Preview Abstract] |
Saturday, October 28, 2006 2:36PM - 2:48PM |
HF.00004: No-core shell model in an EFT framework Ionel Stetcu, Juhani L. Torkkola, Bruce R. Barrett, Ubirajara van Kolck Based on an effective field theory (EFT) that integrates out the pions as degrees of freedom (pionless theory), we present a new approach to the derivation of effective interactions suitable for many-body calculations by means of the no-core shell model. The main investigation is directed toward the description of two-body scattering observables in a restricted harmonic oscillator (HO) basis, and the inherent Gibbs oscillation problem which arises from the truncation of the Hilbert space using HO wave functions. Application of the effective interactions to the description of $^4$He will be discussed. I.S. J.L.T, and B.R.B. acknowledge partial support by NSF grant numbers PHY0070858 and PHY0244389. U.v.K. acknowledges partial support from DOE grant number DE-FG02-04ER41338 and from the Sloan Foundation. [Preview Abstract] |
Saturday, October 28, 2006 2:48PM - 3:00PM |
HF.00005: Relativistic Effects in First Order Three-Body Calculations T. Lin, Ch. Elster, W. Polyzou, W. Gloeckle The Faddeev equation for three-body scattering including relativistic features is directly formulated in momentum space without employing the partial wave decomposition. Based on a Malfliet-Tjon-type potential, the observables of three-body scattering are calculated in first order. The relativistic features considered are kinematics and boost effects, and are examined within the frame work of Poincar\'{e} invariant quantum mechanics. Differential cross sections for elastic and break-up scattering are calculated at selected energies up the GeV scale and compared to the corresponding nonrelativistic cross sections. [Preview Abstract] |
Saturday, October 28, 2006 3:00PM - 3:12PM |
HF.00006: A closed form inverse scattering scheme for the Dirac equation at fixed energy Helmut Leeb, Harald Lehninger, Christian Schilder A new hierarchy of Dirac equations with spherically symmetric scalar and fourth component vector potentials is presented, for which closed form expressions for the solutions, the potentials and the S-matrix can be given in terms of solutions of an original Dirac equation. The hierarchy is generated via a generalized translation operator for the Dirac equation. Using these transformations an inverse scattering scheme has been constructed for the Dirac equation which is the analog to the rational scheme in the non-relativistic case. The method provides for the first time an inversion scheme with closed form expressions for the S-matrix for non-relativistic scattering problems with central and spin-orbit potentials. The inversion scheme was numerically implemented and its features are studied in several examples. [Preview Abstract] |
Saturday, October 28, 2006 3:12PM - 3:24PM |
HF.00007: Low Energy Nuclear Reactions Explained by Nuclear Oscillation--The End of Tunnelling Stewart Brekke Low energy nuclear reactions can be explained through a nuclear oscillation factor using classical mechanics eliminating the need for a tunnelling explanation. Consider an incoming positive charge approaching vibrating nucleus. If the amplitudes of oscillating are equal in all directions and x the position of the incoming charge to the nucleus, then the position of the particle is r = [(x + AcosX)$^2$ + (AcosY)$^2$ + (AcosZ)$^2$]$^{1/2}$. Then KE needed = Barrier Height = kQ(n)q(i)/[(x + AcosX)$^2$ + (AcosY)$^2$ + (AcosZ)$^2$]$^{1/2}$. If the nuclear reaction takes place on the x-axis and contact with the nuclear surface is considered to be contact with the nuclear well, x = AcosX, the magnitude for r after collecting terms is r = [4(AcosX)$^2$ + (AcosY)$^2$ + (Acos Z)$^2$]$^{1/2}$. The KE needed to mount the barrier height is KE = kQ(n)q(i)/[4(AcosX)$^2$ + (AcosY)$^2$ + (Acos Z)$^2$]$^{1/2}$. If the maximum for all cos values is +1 and for all minimum values is -1, r = (6)$^{1/2}$A. and average cos value is RMScos = (1/2)$^{1/2}$, r = (3)$^{1/2}$A. For a static nucleus r = 0. The barrier height minimum is KE = kQ(n)q(i)/(6)$^{1/2}$A, maximun KE = kQ(n)q(i)/0 and average KE = k(q(n)q(i)/(3)$^{1/2}$A. Therefore the Coulomb barrier is different at different times accounting classically for all nuclear reactions. [Preview Abstract] |
Saturday, October 28, 2006 3:24PM - 3:36PM |
HF.00008: Understanding in-medium hadronic interactions through the nuclear equation of state Plamen Krastev, Francesca Sammarruca The relation between energy/particle and density, known as the nuclear equation of state (EOS), plays a major role in a variety of nuclear and astrophysical systems. Spin- and isospin- asymmetries can have a dramatic impact on the equation of state and potentially alter its stability conditions. An example is the possible manifestation of ferromagnetic instabilities, which would signal the existence, at some density, of a spin-polarized state with lower energy than the unpolarized one. This issue is being discussed extensively in the literature and the conclusions are presently very model dependent. We will present and discuss recent progress in our study of highly asymmetric neutron/nuclear matter, in particular spin-polarized matter. The approach we take is microscopic in that the EOS properties are derived from realistic free-space nucleon-nucleon interactions. This makes it possible to understand the nature of the predicted EOS in terms of specific features of the nuclear force and the applied medium effects. [Preview Abstract] |
Saturday, October 28, 2006 3:36PM - 3:48PM |
HF.00009: ABSTRACT WITHDRAWN |
Saturday, October 28, 2006 3:48PM - 4:00PM |
HF.00010: Loop Corrections in Quantum Hadrodynamics Jeff McIntire Although one-loop calculations provide a realistic description of bulk and single-particle nuclear properties, it is necessary to examine loop corrections to develop a systematic finite-density power-counting scheme for the nuclear many-body problem when loops are included. Moreover, it is still imperative to study exchange and correlation corrections systematically, in order to make reliable predictions for other nuclear observables. One must also verify that the natural sizes of the one-loop parameters are not destroyed by explicit inclusion of many-body corrections. The loop expansion is applied to our chiral QHD lagrangian; with the techniques of Infrared Regularization, we found that it is possible to separate out the short-range contributions and to write them as products of fields that are already present in our lagrangian. (The appropriate field variables must be re-defined at each order in loops.) The corresponding parameters implicitly include short-range effects to all orders in the interaction, so these effects need not be calculated explicitly. The remaining (long-range) contributions that must be calculated resemble those in conventional nuclear-structure calculations (e.g. ladders, rings, etc.). [Preview Abstract] |
Saturday, October 28, 2006 4:00PM - 4:12PM |
HF.00011: ABSTRACT WITHDRAWN |
Saturday, October 28, 2006 4:12PM - 4:24PM |
HF.00012: ABSTRACT WITHDRAWN |
Saturday, October 28, 2006 4:24PM - 4:36PM |
HF.00013: Density Functional Theory Approach to Shell Model Hamiltonians Mihai Horoi Density Functional Theory (DFT) is a well established method of obtaining ground state (g.s.) energies and one-body densities for systems of interacting fermions, such as electron and nucleons. DFT is mostly used in nuclear physics via short-range, Skyrme-type, interactions in coordinate space. We investigate a different density functional approach in finite model spaces, specific to shell model calculations. We attempt to extract the density functional form and the associated parameters in a fixed model space, by comparing the DFT results with the exact shell model calculations for small number of particles/holes. We than use the density functional to calculate cases with more particles that are more challenging for the shell model. Examples in the sd and fp model spaces will be presented. [Preview Abstract] |
Saturday, October 28, 2006 4:36PM - 4:48PM |
HF.00014: Nuclear shadowing at small Bjorken-x from diffractive scattering Adeola Adeluyi, George Fai We calculate the nuclear shadowing ratio at small Bjorken-x for nuclei in the mass range $4 \leq A \leq 240$. We work in the kinematic regime relevant to small-x shadowing data of both the NMC and E665 experiments. The diffractive dissociation cross section, which is an input to our calculation, is parameterized separating the low-mass resonances and the high-mass continuum, following the H1 collaboration [1], using data from FNAL [2]. Our calculated results are in reasonable agreement with the NMC/E665 data at $x \approx 10^{-4}$, indicating the applicability of generalized Gribov theory.\\[2ex] 1. C. Adloff {\it et al.} [H1 Collaboration], Z. Phys. C {\bf 74}, 221 (1997).\\ 2. T.J. Chapin {\it et al.}, Phys. Rev. D {\bf 31}, 17 (1995). [Preview Abstract] |
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