Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session X13: Nuclear Theory IILive
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Sponsoring Units: DNP Chair: Charlotte Elster, Ohio U |
Tuesday, April 20, 2021 10:45AM - 10:57AM Live |
X13.00001: Charge radii of exotic neon and magnesium isotopes Thomas Papenbrock, Gaute Hagen, Gustav R Jansen, Sam J Novario We compute the charge radii of even-mass neon and magnesium isotopes from neutron number N = 8 to the dripline. Our calculations are based on nucleon-nucleon and three-nucleon potentials from chiral effective field theory that include delta isobars. These potentials yield an accurate saturation point and symmetry energy of nuclear matter. We use the coupled-cluster method based on an axially symmetric reference state. Binding energies and two-neutron separation energies largely agree with data and the dripline in neon is accurate. The computed charge radii have an estimated uncertainty of about 2-3 percent and are accurate for many isotopes where data exist. Finer details such as isotope shifts, however, are not accurately reproduced. Chiral potentials correctly yield the subshell closure at N = 14 and also a decrease in charge radii at N = 8 (observed in neon and predicted for magnesium). They yield a continued increase of charge radii as neutrons are added beyond N = 14 yet underestimate the large increase at N = 20 in magnesium. Work available as [S. J. Novario, G. Hagen, G. R. Jansen, T. Papenbrock, Phys. Rev. C 102, 051303 (2020); arXiv:2007.06684]. [Preview Abstract] |
Tuesday, April 20, 2021 10:57AM - 11:09AM Live |
X13.00002: Coupled cluster calculation of deformed nuclei. Zhonghao Sun, Thomas Papenbrock, Gaute Hagen We studied the ground states of deformed nuclei with the coupled-cluster method. The reference state of the nuclei is generated by deformed Hartree-Fock using the newly developed chiral potential including the $\Delta $ degree of freedom. The normal ordered interaction is transformed into a natural orbit and then truncated to affordable model space. We performed coupled-cluster calculation without symmetry restoration based on the fact that the uncertainties for lacking angular momentum projection are identical to that from triple up to A-particle-A-hole excitations, which is well controlled in the coupled-cluster theory. We calculated the ground state energy and charge radii of even-even nuclei from Z$=$20-30 and N$=$24-40 and have good agreement with the data. [Preview Abstract] |
Tuesday, April 20, 2021 11:09AM - 11:21AM Live |
X13.00003: Angular momentum projection in coupled-cluster theory Gaute Hagen, Zhonghao Sun, Sam Novario, Thomas Papenbrock, Thomas Duguet, Alexander Tichai Atomic nuclei have good spin, parity, and third component of the isospin. Yet for many nuclei, symmetry unrestricted mean-field calculations find it advantageous to break rotational invariance and particle number conservation such that the vacuum states accurately reflect the emergent symmetry breaking of intrinsically deformed and superfluid nuclei, respectively. Starting from such symmetry-breaking mean-field states in nuclear structure computations has the advantage that less effort needs to be spent in including correlations beyond the mean field; the disadvantage consists in the need to perform symmetry projections. In this talk I will present the first implementation and application of symmetry restoration in axially deformed coupled-cluster calculations. I will show results for the prototypical deformed nuclei 8-Be and 20-Ne and compare with data and other existing calculations. [Preview Abstract] |
Tuesday, April 20, 2021 11:21AM - 11:33AM Live |
X13.00004: Using Similarity Renormalization Group Methods to Analyze Optical Potentials Mostofa Hisham, Anthony Tropiano, R.J. Furnstahl Similarity Renormalization Group (SRG) operations evolve Hamiltonians by continuous unitary transformations, driving hard potentials to softer potentials by decoupling high- and low-momentum components. Using a toy model, we examine properties of the optical potential through SRG transformations and study the effects of commonly used approximation methods on the SRG-evolved potential. We also examine the prospects for using the SRG to decouple the projectile and target in high energy scattering. Finally, we extend the construction and analysis of low-resolution optical potentials from more general potentials including three-body interactions. [Preview Abstract] |
Tuesday, April 20, 2021 11:33AM - 11:45AM Live |
X13.00005: Pauli energy contribution to nucleus-nucleus interaction potentials Sait Umar, Kyle Godbey, Cedric Simenel In this work we use the nucleon localization function (NLF) approach [1] to demonstrate the contribution of Pauli energy to nucleus-nucleus interaction potentials. This is a follow up on our previous work on assessing the Pauli effect on the formation of potential pockets in ion-ion interaction potentials [2]. Calculations are done using the density-constrained frozen density approach (DCFHF), the dynamical time-dependent density-constrained Hartree-Fock (DC-TDHF) method, as well as the full time-dependent Hartree-Fock (TDHF) method. We also utilize the Pauli localization function (PLF) to better visualize these effects. [1] T. Li, M. Z. Chen, C. L. Zhang, W. Nazarewicz, and M. Kortelainen, Nucleon localization function in rotating nuclei, Phys. Rev. C 102, 044305 (2020). [2] C. Simenel, A. S. Umar, K. Godbey, M. Dasgupta, and D. J. Hinde, How the Pauli exclusion principle affects fusion of atomic nuclei, Phys. Rev. C 95, 031601 (2017). [Preview Abstract] |
Tuesday, April 20, 2021 11:45AM - 11:57AM Live |
X13.00006: Microscopic origin of reflection-asymmetric nuclear shapes Mengzhi Chen, Tong Li, Jacek Dobaczewski, Witold Nazarewicz The existence of nuclei with stable reflection-asymmetric ground-state (g.s.) shapes has been supported by rich experimental evidence. Theoretically, a recent survey systematically predicts the regions of pear-liked shapes in the regions where the doublets of opposite parity shells with $\Delta\ell=\Delta j=3$ can be found. In our work, we investigate even-even Ba, Ra, U and Yb isotopes in the framework of the Skyrme-Hartree-Fock-Bogoliubov theory. We study neutron-proton, neutron-neutron, and proton-proton multipole interaction energies and analyze their role in the onset of reflection-asymmetric deformations. We demonstrate that reflection-asymmetric deformations are driven by the neutron-proton part of the nuclear interaction energy of odd multipolarity. We also show that the small reflection-asymmetric deformation energies result from strong cancellations between even- and odd- multipolarity components of the nuclear binding energy. Therefore, high-multipolarity components, especially $\lambda = 5$, are crucial for the appearance of stable reflection-asymmetric deformations. [Preview Abstract] |
Tuesday, April 20, 2021 11:57AM - 12:09PM Live |
X13.00007: Symplectic Effective Field Theory David Kekejian, Jerry Draayer, Kristina Launey We explore the emergence of symplectic Sp(3,R) symmetry, a dynamical symmetry that is commonly displayed in atomic nuclei, from an effective quantum field theory. Starting from a simple extension to the harmonic oscillator Lagrangian, we construct an effective field theory that yields a quantum mechanical Hamiltonian that is Sp(3,R)-symmetric in nature. The application of this Hamiltonian to various light nuclei produces reasonable energy spectra, B(E2) strengths and radii. [Preview Abstract] |
Tuesday, April 20, 2021 12:09PM - 12:21PM Live |
X13.00008: Unmixing Symmetries Calvin Johnson The low-lying spectra of atomic nuclei display diverse behaviors, for example rotational bands, which can be described phenomenologically by simple symmetry groups such as spatial SU(3). This leads to the idea of \textit{dynamical symmetry}. Detailed microscopic calculations, however, show these symmetries are in fact often strongly mixed and the wave function fragmented across many irreps. More commonly the fragmentation across members of a band are similar, which is called a \textit{quasi-dynamical symmetry}. I numerically construct unitary transformations from a quasi-dynamical symmetry to a dynamical symmetry, adapting the \textit{similarity renormalization group,} or SRG, in order to transform away the symmetry-mixing parts of the Hamiltonian, transforms a quasi-dynamical symmetry to a dynamical symmetry, that is, unmixes the mixed symmetries. [Preview Abstract] |
Tuesday, April 20, 2021 12:21PM - 12:33PM Live |
X13.00009: Statistical properties of nuclei in the static-path plus random-phase approximation Paul Fanto, Yoram Alhassid Nuclear level densities and $\gamma$-ray strength functions ($\gamma$SFs) are important inputs to the Hauser-Feshbach theory of compound-nucleus reactions. To calculate these statistical properties, we apply the static-path plus random-phase approximation (SPA+RPA), which includes large-amplitude static fluctuations and small-amplitude quantal fluctuations beyond the mean field. We find excellent agreement between SPA+RPA state densities and exact state densities calculated with the shell model Monte Carlo (SMMC) method in lanthanide nuclei [1]. We also discuss a computational method to extend SPA+RPA calculations to larger model spaces. In addition, we benchmark finite-temperature SPA+RPA $E2$ and $M1$ $\gamma$SFs by comparing them with exact configuration-interaction (CI) shell model and quasiparticle random-phase approximation (QRPA) $\gamma$SFs in $sd$ shell nuclei. We find that the SPA+RPA reproduces qualitative aspects of the exact CI shell model results. We discuss the current limitations of the SPA+RPA for $\gamma$SFs and outline possible extensions of this method. [1] P. Fanto and Y. Alhassid, arXiv:2008.13722. [Preview Abstract] |
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