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Nuclear Theory·nucl-th

Thursday·August 24, 2017

11 papers—5 primary·6 cross-listed

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  1. 01

    Towards an understanding of discrete ambiguities in truncated partial wave analyses

    Y. Wunderlich · A. Švarc · R. L. Workman · L. Tiator · R. Beck

    It is well known that the observables in a single-channel scattering problem remain invariant once the amplitude is multiplied by an overall energy- and angle-dependent phase. This invariance is called the continuum ambiguity and acts on the infinite partial wave set. It has also long been known that, in the case of a truncated partial wave set, another invariance exists, originating from the replacement of the roots of partial wave amplitudes with their complex conjugate values. This discrete ambiguity is also known as the Omelaenko-Gersten-type ambiguity. In this paper, we show that for scalar particles, discrete ambiguities are just a subset of continuum ambiguities with a specific phase and thus mix partial waves, as the continuum ambiguity does. We present the main features of both, continuum and discrete ambiguities, and describe a numerical method which establishes the relevant phase connection.

    nucl-thPRC(2017)·17 citations
  2. 02

    Multipole modes of excitation in triaxially deformed superfluid nuclei

    Kouhei Washiyama · Takashi Nakatsukasa

    The five-dimensional quadrupole collective model based on energy density functionals (EDF) has often been employed to treat long-range correlations associated with shape fluctuations in nuclei. Our goal is to derive the collective inertial functions in the collective Hamiltonian by the local quasiparticle random phase approximation (QRPA) that correctly takes into account time-odd mean-field effects. Currently, practical framework to perform the QRPA calculation with the modern EDFs on the deformation space is not available. Toward this goal, we develop an efficient numerical method to perform the QRPA calculation on the deformation space based on the Skyrme EDF. We use the finite amplitude method (FAM) for efficient calculation of QRPA strength functions for multipole external fields. We construct a computational code of FAM-QRPA in the three-dimensional Cartesian coordinate space to handle triaxially deformed superfluid nuclei. We validate our new code by comparing our results with former QRPA calculations for axially symmetric nuclei. Isoscalar quadrupole strength functions in triaxial superfluid nuclei, Ru and Pt, are obtained within a reasonable computational cost. QRPA calculations for triaxially deformed superfluid nuclei based on the Skyrme EDF are achieved with the help of FAM. This is an important step toward the microscopic calculation of collective inertial functions of the local QRPA.

    nucl-thPRC(2017)·16 citations
  3. 03

    The equation of state for dense nucleonic matter from a metamodeling. I. Foundational aspects

    J. Margueron🇺🇸 · R. Hoffmann Casali🇫🇷 · F. Gulminelli🇫🇷

    A metamodeling for the nucleonic equation of state (EOS), inspired from a Taylor expansion around the saturation density of symmetric nuclear matter, is proposed and parameterized in terms of the empirical parameters. The present knowledge of nuclear empirical parameters is first reviewed in order to estimate their average values and associated uncertainties, and thus defining the parameter space of the metamodeling. They are divided into isoscalar and isovector type, and ordered according to their power in the density expansion. The goodness of the metamodeling is analyzed against the predictions of the original models. In addition, since no correlation among the empirical parameters is assumed a priori, all arbitrary density dependences can be explored, which might not be accessible in existing functionals. Spurious correlations due to the assumed functional form are also removed. This meta-EOS allows direct relations between the uncertainties on the empirical parameters and the density dependence of the nuclear equation of state and its derivatives, and the mapping between the two can be done with standard Bayesian techniques. A sensitivity analysis shows that the more influential empirical parameters are the isovector parameters and , and that laboratory constraints at super-saturation densities are essential to reduce the present uncertainties. The present metamodeling for the EOS for nuclear matter is proposed for further applications in neutron stars and supernova matter.

    nucl-thPRC(2018)·331 citations
  4. 04

    The equation of state for dense nucleonic matter from a meta-modeling. II. Predictions for neutron stars properties

    J. Margueron🇺🇸 · R. Hoffmann Casali🇫🇷 · F. Gulminelli🇫🇷

    Employing a recently proposed metamodeling for the nucleonic matter equation of state we analyze neutron star global properties such as masses, radii, momentum of inertia, and others. The impact of the uncertainty on empirical parameters on these global properties is analyzed in a Bayesian statistical approach. Physical constraints, such as causality and stability, are imposed on the equation of state and different hypotheses for the direct Urca (dUrca) process are investigated. In addition, only metamodels with maximum masses above 2 are selected. Our main results are the following: the equation of state exhibits a universal behavior against the dUrca hypothesis under the condition of charge neutrality and -equilibrium; neutron stars, if composed exclusively of nucleons and leptons, have a radius of 12.70.4~km for masses ranging from 1 up to 2; a small radius lower than 11~km is very marginally compatible with our present knowledge of the nuclear empirical parameters; and finally, the most important empirical parameters which are still affected by large uncertainties and play an important role in determining the radius of neutrons stars are the slope and curvature of the symmetry energy ( and ) and, to a lower extent, the skewness parameters ().

    nucl-thPRC(2018)·200 citations
  5. 05

    Electric dipole strength and dipole polarizability in Ca within a fully self-consistent second random-phase approximation

    Danilo Gambacurta🇷🇴 · Marcella Grasso🇫🇷 · Olivier Vasseur🇫🇷

    The second random-phase-approximation model corrected by a subtraction procedure designed to cure double counting, instabilities, and ultraviolet divergences, is employed for the first time to analyze the dipole strength and polarizability in Ca. All the terms of the residual interaction are included, leading to a fully self-consistent scheme. Results are illustrated with two Skyrme parametrizations, SGII and SLy4. Those obtained with the SGII interaction are particularly satisfactory. In this case, the low-lying strength below the neutron threshold is extremely well reproduced and the giant dipole resonance is described in a very satisfactory way especially in its spreading and fragmentation. Spreading and fragmentation are produced in a natural way within such a theoretical model by the coupling of 1 particle-1 hole and 2 particle-2 hole configurations. Owing to this feature, we may provide for the electric polarizability as a function of the excitation energy a curve with a similar slope around the centroid energy of the giant resonance compared to the corresponding experimental results. This represents a considerable improvement with respect to previous theoretical predictions obtained with the random-phase approximation or with several ab-initio models. In such cases, the spreading width of the excitation cannot be reproduced and the polarizability as a function of the excitation energy displays a stiff increase around the predicted centroid energy of the giant resonance.

    nucl-thnucl-exPLB(2018)·32 citations

Affiliations

first authorsco-authorsvia INSPIRE