Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session LM: Nuclear Theory VI |
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Chair: Charlotte Elster, Ohio University Room: White Hill |
Wednesday, October 13, 2021 2:00PM - 2:12PM |
LM.00001: Nuclear EDFs: Particle vibration coupling in superfluid nuclei with axial deformation Yinu Zhang, Elena Litvinova The nuclear density functional theory (DFT) has demonstrated the ability to provide a fairly accurate description of nuclear ground-state properties and low-energy collective excitations across the nuclear chart. In this work, we elaborate on the particle-vibration coupling (PVC), which is associated with the leading correlations beyond the mean-field approximation in strongly-coupled many-body fermionic systems treated within a consistent and systematic framework of the equation of motion method. For deformed nuclei, the conventional solution of the quasiparticle random phase approximation (QRPA), which provides the major input for the PVC, requires prohibitive numerical efforts. By linking the notion of the quasiparticle-phonon vertex to the variation of the Bogoliubov's Hamiltonian, we show that the recently developed finite-amplitude method (FAM) can be efficiently employed to compute the PVC vertices within the FAM-QRPA for deformed nuclei. To illustrate the validity of the particle vibration coupling to superfluid nuclei in axial deformation, the calculations based on the relativistic density-dependent point-coupling Lagrangian are performed for the single-nucleon states as well as the giant resonances in medium-mass and heavy nuclei with axial deformations. The results show considerable improvement compare with experimental data for axially-deformed nuclei. |
Wednesday, October 13, 2021 2:12PM - 2:24PM |
LM.00002: Eigenvector Continuation for Resonance States Nuwan Yapa, Sebastian Koenig Eigenvector continuation (EC) has emerged as an intriguing method to yield approximate solutions for computationally expensive eigenvalue problems with great speed and accuracy. With EC, the essence of a quantum system is "learned" through the construction of a highly effective (non-orthogonal) basis, leading to a variational calculation of the states of interest with rapid convergence. Extracting resonance energies of few-body systems is of great importance in nuclear physics, but it continues to pose challenges due to the large computational complexity involved. In this work we study EC as an option to facilitate such calculations. To that end, we use both finite-volume techniques, where resonances are manifest as avoided crossings of energy levels, as well as direct studies in momentum space, where resonances can be identified after analytic continuation of the Schrödinger equation. In both cases we find that EC makes it possible to extrapolate trajectories of resonance states. In particular, we discuss the possibility of predicting resonances based on bound training states alone, tracing their transition into the continuum as a parameter in the Hamiltonian is varied. |
Wednesday, October 13, 2021 2:24PM - 2:36PM |
LM.00003: Shell Model Monte Carlo Studies of Collectivity in Heavy Nuclei Sohan Vartak, Yoram Alhassid, Marco Bonett-Matiz A microscopic description of the crossover from vibrational to rotational collectivity in heavy nuclei in the configuration-interaction shell model approach is beyond the reach of conventional diagonalization methods due to combinatorial growth of the many-particle model space with the number of valence nucleons and/or valence single-particle orbitals. The shell model Monte Carlo (SMMC) method is viable in such model spaces, and has been successfully applied to calculate thermal and ground-state observables. Recently, a method has been developed that provides access to spectral information encoded in a generalized eigenvalue problem satisfied by imaginary-time response matrices of one-body densities [1]. We have validated the method in an sd-shell nucleus whose excitation energies can be calculated exactly using conventional diagonalization techniques. Application of this method to chains of heavy lanthanide isotopes enables the calculation of a few energy levels for each spin and parity, yielding direct spectral evidence of the crossover from vibrational to rotational collectivity. The generalized eigenvalue problem also encodes information about one-body transition densities, and we discuss extensions of the method to extract this information. |
Wednesday, October 13, 2021 2:36PM - 2:48PM |
LM.00004: Global consequences of removing parametric correlations in covariant energy density functionals. Ahmad Taninah, Anatoli Afanasjev Covariant density functional theory (CDFT) is one of the modern theoretical tools for the description of finite nuclei and neutron stars. Its performance is defined by underlying covariant energy density functionals (CEDFs) which depend on several parameters. The analysis of the major classes of CEDFs reveals the existence of parametric correlations between these parameters [1,2]. The removal of these correlations reduces the number of independent parameters to five or six depending on the underlying functional structure. However, this analysis is based on the fitting protocols which employ only spherical nuclei. In the present contribution, we investigated the consequences of the removal of parametric correlations to full nuclear landscape for which experimental data are available [3]. It is shown that the removal of parametric correlations does not lead to a degradation of the performance of CEDFs on a global scale. Moreover, this study also reveals the need to include information on deformed nuclei for the improvement of fitting protocols. In addition, the asymptotic behavior of the basis truncation on the physical observables of interest has been analyzed. It also reveals that for a comparable accuracy description a larger basis is needed in deformed nuclei as compared with spherical ones. |
Wednesday, October 13, 2021 2:48PM - 3:00PM |
LM.00005: Extremely proton rich nuclei: rotation-induced proton halos and extension of nuclear landscape beyond spin zero limit. saja A Teeti, Ahmad Taninah, Anatoli Afanasjev Recent investigations reveal a number of physical mechanisms by which it is |
Wednesday, October 13, 2021 3:00PM - 3:12PM |
LM.00006: Toward emulating nuclear reactions using eigenvector continuation. Pablo G Giuliani, Christian Drischler, Amy E Lovell, Michael Quinonez, Filomena Nunes We construct an efficient emulator for two-body scattering using the generalized Kohn variational principle and trial wave functions derived from eigenvector continuation. Our emulator simultaneously applies an array of Kohn variational principles with different asymptotic boundary conditions, which allows for detection and removal of spurious singularities known as Kohn anomalies. We then perform a Bayesian analysis of elastic scattering of neutrons off $^{40}$Ca and $^{208}$Pb nuclei using realistic optical potentials. The emulator’s high accuracy and computational speed enable rigorous uncertainty quantification for improving optical potentials in the FRIB era. |
Wednesday, October 13, 2021 3:12PM - 3:24PM |
LM.00007: Extending the limits of nuclear landscape via new physical mechanisms Anatoli Afanasjev, Sylvester E Agbemava, Ahmad Taninah, saja A Teeti The detailed investigation of new physical mechanisms which allow to extend the boundaries of |
Wednesday, October 13, 2021 3:24PM - 3:36PM |
LM.00008: A Hyperspherical Treatment of Reaction Pathways in Few-Nucleon Systems Michael D Higgins, Chris H Greene The adiabatic hyperspherical representation has been extensively applied to few–body systems, in which hyperspherical potentials and couplings describe all possible reaction pathways on an equal footing through an adiabatic collective coordinate, the hyperradius. In addition to providing qualitative insight about the pathways controlling key reaction and resonance phenomena, the hyperspherical potentials plus non–adiabatic couplings can provide a quantitative description of reaction rates, bound states and resonances. In this work, reaction pathways for the three–body nnp, npp (J^{π}=1/2^{+},T=1/2) and four–body nnpp (J^{π}=0^{+},T=0) systems are visualized through a spectrum of hyperspherical potential curves, which show the different ways these interacting systems can fragment into bound and continuum channels. Calculations are preformed using adiabatic hyperspherical methods that implement an explicitly–correlated Gaussian basis (Suzuki et. al., Few Body Syst. (2008) 42: 33–72). Two different nucleon–nucleon (NN) interactions are considered, the Minnesota NN interaction, and the realistic AV8' NN interaction with a spin–independent three–nucleon force (Hiyama, E. et al., Phys. Rev. C. 70, 031001(2004)). In addition, three– and four–nucleon binding energies and resonances are computed. |
Wednesday, October 13, 2021 3:36PM - 3:48PM |
LM.00009: Real time dynamics of gauge field theory with truncated Hamiltonian methods Ivan Kukuljan, Gábor Takács, Spyros Sotiriadis Truncated Hamiltonian methods (THM) have been studied as a powerful complement to lattice methods for the study of strongly coupled quantum field theory (QFT). THM have been used to compute spectra of the models, properties of bound states, symmetry breaking, (higher order) correlation functions, quantum chaos and particularly excel at real time evolution, a task difficult for Monte Carlo methods. They do not require a discretization of space-time and have been successfully applied to systems in 1 and 2 spatial dimensions. |
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