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Nuclear Theory·nucl-th

Monday·January 28, 2019

7 papers—3 primary·4 cross-listed

All7Primary3Cross-lists4
  1. 01

    Microscopic multiphonon approach to nuclei with a valence hole in the oxygen region

    Giovanni De Gregorio · Frantisek Knapp · Nicola Lo Iudice · Petr Vesely

    An equation of motion phonon method, developed for even nuclei and recently extended to odd systems with a valence particle, is formulated in the hole-phonon coupling scheme and applied to A=15 and A=21 isobars with a valence hole. The method derives a set of equations which yield an orthonormal basis of states composed of a hole coupled to an orthonormal basis of correlated n-phonon states (n = 0, 1, 2, . . .), built of constituent Tamm-Dancoff phonons, describing the excitations of a doubly magic core. The basis is then adopted to solve the full eigenvalue problem. The method is formally exact but lends itself naturally to simplifying approximations. Self-consistent calculations using a chiral Hamiltonian in a space encompassing up to two-phonon and three-phonon basis states in A=21 A=15 nuclei, respectively, yield full spectra, moments, electromagnetic and beta-decay transition strengths, and electric dipole cross sections. The analysis of the hole-phonon composition of the eigenfunctions contributes to clarify the mechanism of excitation of levels and resonances and to understand the reasons of the deviations of the theory from the experiments. Prescriptions for reducing these discrepancies are suggested.

    nucl-th0 citations
  2. 02

    Scaling Properties of the Lipkin Model at the Critical Point

    J.M. Arias · J.E. García-Ramos

    The influence of Franco Iachello in Physics during the last 50 years and, in particular, in the use of algebraic methods applied to very different physical problems has been broad, extense and have permeated most branches of Physics, from Nuclear and Molecular to Particle and Condensed Matter physics. Apart of many other contributions, at the beginning of the 2000's he introduced the concept of critical point symmetry and triggered the study of the many faces of quantum phase transitions in nuclei and other mesoscopic systems. In this contribution, we present the analysis of the scaling properties of the Lipkin model spectrum at the phase transition point and we focus on the differences between first and second order quantum phase transitions. Moreover, we explain how the obtained results can be also of application for the interacting boson model.

    nucl-thAIP Conf.Proc.(2019)·0 citations
  3. 03

    Critical view of nonlocal nuclear potentials in alpha decay

    J. E. Perez Velasquez · N. G. Kelkar · N. J. Upadhyay

    Different models for the nonlocal description of the nuclear interaction are compared through a study of their effects on the half-lives of radioactive nuclei decaying by the emission of alpha particles. The half-lives are evaluated by considering a pre-formed alpha particle (He nucleus) which tunnels through the Coulomb barrier generated by its interaction with the daughter nucleus. An effective potential obtained from a density dependent double folding strong potential between the alpha and the daughter nucleus within the nonlocal framework is found to decrease the half-lives as compared to those in the absence of nonlocalities. Whereas the percentage decrease within the older Perey-Buck and São Paulo models ranges between 20 to 40\% for medium to heavy nuclei, a recently proposed effective potential leads to a decrease of only 2 - 4 \%. In view of these results, we provide a closer examination of the approximations used in deriving the local equivalent potentials and propose that apart from the scattering data, the alpha decay half-lives could be used as a complementary tool for constraining the nonlocality models.

    nucl-thnucl-exPRC(2019)·16 citations
  4. 04

    Dynamical systems and nonlinear transient rheology of the far-from-equilibrium Bjorken flow

    Alireza Behtash🇺🇸 · Syo Kamata🇺🇸 · M. Martinez🇺🇸 · Haosheng Shi🇺🇸

    In relativistic kinetic theory, the one-particle distribution function is approximated by an asymptotic perturbative power series in Knudsen number which is divergent. For the Bjorken flow, we expand the distribution function in terms of its moments and study their nonlinear evolution equations. The resulting coupled dynamical system can be solved for each moment consistently using a multi-parameter transseries which makes the constitutive relations inherit the same structure. A new non-perturbative dynamical renormalization scheme is born out of this formalism that goes beyond the linear response theory. We show that there is a Lyapunov function, aka dynamical potential, which is, in general, a function of the moments and time satisfying Lyapunov stability conditions along RG flows connected to the asymptotic hydrodynamic fixed point. As a result, the transport coefficients get dynamically renormalized at every order in the time-dependent perturbative expansion by receiving non-perturbative corrections present in the transseries. The connection between the integration constants and the UV data is discussed using the language of dynamical systems. Furthermore, we show that the first dissipative correction in the Knudsen number to the distribution function is not only determined by the known effective shear viscous term but also a new high energy non-hydrodynamic mode. It is demonstrated that the survival of this new mode is intrinsically related to the nonlinear mode-to-mode coupling with the shear viscous term. Finally, we comment on some possible phenomenological applications of the proposed non-hydrodynamic transport theory.

    ↳ hep-thhep-phnucl-thPRD(2019)·67 citations
  5. 05

    NCrystal : a library for thermal neutron transport

    Xiao-Xiao Cai · Thomas Kittelmann

    An open source software package for modelling thermal neutron transport is presented. The code facilitates Monte Carlo-based transport simulations and focuses in the initial release on interactions in both mosaic single crystals as well as polycrystalline materials and powders. Both coherent elastic (Bragg diffraction) and incoherent or inelastic (phonon) scattering are modelled, using basic parameters of the crystal unit cell as input. Included is a data library of validated crystal definitions, standalone tools and interfaces for C++, C and Python programming languages. Interfaces for two popular simulation packages, Geant4 and McStas, are provided, enabling highly realistic simulations of typical components at neutron scattering instruments, including beam filters, monochromators, analysers, samples and detectors. All interfaces are presented in detail, along with the end-user configuration procedure which is deliberately kept user-friendly and consistent across all interfaces. An overview of the relevant neutron scattering theory is provided, and the physics modelling capabilities of the software are discussed. Particular attention is given here to the ability to load crystal structures and form factors from various sources of input, and the results are benchmarked and validated against experimental data and existing crystallographic software. Good agreements are observed.

    ↳ physics.comp-phcond-mat.mtrl-scinucl-exnucl-thComput.Phys.Commun.(2020)·30 citations
  6. 06

    Neutron production from thermonuclear reactions in laser-generated plasmas

    Yuanbin Wu🇩🇪

    The production of intense neutron beams via thermonuclear reactions in laser-generated plasmas is investigated theoretically. So far, state-of-the-art neutron beams are produced via laser-induced particle acceleration leading to high-energy particle beams that subsequently interact with a secondary target. Here we show that neutron beams of two orders of magnitude narrower bandwidth can be obtained from thermonuclear reactions in plasmas generated by Petawatt-class lasers. The intensity of such neutron beams is about one or two orders of magnitude lower than the one of the state-of-the-art laser-driven neutron beams. We study to this end the reaction H(, )He in plasmas generated by Petawatt-class lasers interacting with D gas jet targets and CD solid-state targets. The results also shows the possibility of direct measurements of reaction rates at low temperatures of astrophysical interests. In addition, the use of CD solid-state targets can also lead to great enhancements on the plasma screening compared to the case of D gas jet targets, opening new possibilities to study this so far unsolved issue in the field of astrophysics.

    ↳ physics.plasm-phnucl-thPhys.Plasmas(2020)·4 citations
  7. 07

    What does kinematical target mass sensitivity in DIS reveal about hadron structure?

    E. Moffat🇺🇸 · T. C. Rogers🇺🇸 · W. Melnitchouk🇺🇸 · N. Sato🇺🇸 · F. Steffens🇩🇪

    We study the role of purely external kinematical approximations in inclusive deep-inelastic lepton--hadron scattering within QCD factorization, and consider factorization with an exact treatment of the target hadron mass. We discuss how an observed phenomenological improvement obtained by accounting for target mass kinematics could be interpreted in terms of general properties of target structure, and argue that such an improvement implies a hierarchy of nonperturbative scales within the hadron.

    ↳ hep-phnucl-thPRD(2019)·21 citations

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first authorsco-authorsvia INSPIRE