| 1. |
- Ekström, Andreas, 1980, et al.
(author)
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What is ab initio in nuclear theory?
- 2023
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In: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 11
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Research review (peer-reviewed)abstract
- Ab initio has been used as a label in nuclear theory for over two decades. Its meaning has evolved and broadened over the years. We present our interpretation, briefly review its historical use, and discuss its present-day relation to theoretical uncertainty quantification.
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| 2. |
- Hu, Baishan, et al.
(author)
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Ab initio predictions link the neutron skin of Pb-208 to nuclear forces
- 2022
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In: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2481 .- 1745-2473. ; 18:10, s. 1196-1200
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Journal article (peer-reviewed)abstract
- Heavy atomic nuclei have an excess of neutrons over protons, which leads to the formation of a neutron skin whose thickness is sensitive to details of the nuclear force. This links atomic nuclei to properties of neutron stars, thereby relating objects that differ in size by orders of magnitude. The nucleus Pb-208 is of particular interest because it exhibits a simple structure and is experimentally accessible. However, computing such a heavy nucleus has been out of reach for ab initio theory. By combining advances in quantum many-body methods, statistical tools and emulator technology, we make quantitative predictions for the properties of Pb-208 starting from nuclear forces that are consistent with symmetries of low-energy quantum chromodynamics. We explore 10(9) different nuclear force parameterizations via history matching, confront them with data in select light nuclei and arrive at an importance-weighted ensemble of interactions. We accurately reproduce bulk properties of Pb-208 and determine the neutron skin thickness, which is smaller and more precise than a recent extraction from parity-violating electron scattering but in agreement with other experimental probes. This work demonstrates how realistic two- and three-nucleon forces act in a heavy nucleus and allows us to make quantitative predictions across the nuclear landscape. Predictions of the properties of Pb-208 from first principles augmented by statistical learning techniques reproduce those seen in experiments but rule out very thick neutron skins.
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| 3. |
- Jiang, Weiguang, 1989, et al.
(author)
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Accurate bulk properties of nuclei from A=2 to infinity from potentials with Delta isobars
- 2020
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In: Physical Review C. - 2469-9985 .- 2469-9993. ; 102:5
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Journal article (peer-reviewed)abstract
- We optimize Delta-full nuclear interactions from chiral effective field theory. The low-energy constants of the contact potentials are constrained by two-body scattering phase shifts, and by properties of bound state of A = 2 to 4 nucleon systems and nuclear matter. The pion-nucleon couplings are taken from a Roy-Steiner analysis. The resulting interactions yield accurate binding energies and radii for a range of nuclei from A = 16 to A = 132, and provide accurate equations of state for nuclear matter and realistic symmetry energies. Selected excited states are also in agreement with data.
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| 4. |
- Jiang, Weiguang, 1989, et al.
(author)
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Bayesian probability updates using sampling/importance resampling: Applications in nuclear theory
- 2022
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In: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 10
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Journal article (peer-reviewed)abstract
- We review an established Bayesian sampling method called sampling/importance resampling and highlight situations in nuclear theory when it can be particularly useful. To this end we both analyse a toy problem and demonstrate realistic applications of importance resampling to infer the posterior distribution for parameters of ΔNNLO interaction model based on chiral effective field theory and to estimate the posterior probability distribution of target observables. The limitation of the method is also showcased in extreme situations where importance resampling breaks.
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| 5. |
- Jiang, Weiguang, 1989, et al.
(author)
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Emulating ab initio computations of infinite nucleonic matter
- 2024
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In: Physical Review C. - 2469-9985 .- 2469-9993. ; 109:6
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Journal article (peer-reviewed)abstract
- We construct efficient emulators for the ab initio computation of the infinite nuclear matter equation of state. These emulators are based on the subspace-projected coupled-cluster method for which we here develop a new algorithm called small-batch voting to eliminate spurious states that might appear when emulating quantum many-body methods based on a non-Hermitian Hamiltonian. The efficiency and accuracy of these emulators facilitate a rigorous statistical analysis within which we explore nuclear matter predictions for >106 different parametrizations of a chiral interaction model with explicit Δ-isobars at next-to-next-to leading order. Constrained by nucleon-nucleon scattering phase shifts and bound-state observables of light nuclei up to He4, we use history matching to identify nonimplausible domains for the low-energy coupling constants of the chiral interaction. Within these domains we perform a Bayesian analysis using sampling and importance resampling with different likelihood calibrations and study correlations between interaction parameters, calibration observables in light nuclei, and nuclear matter saturation properties.
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| 6. |
- Jiang, Weiguang, 1989, et al.
(author)
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Nuclear-matter saturation and symmetry energy within Δ -full chiral effective field theory
- 2024
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In: Physical Review C. - 2469-9985 .- 2469-9993. ; 109:6
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Journal article (peer-reviewed)abstract
- Nuclear saturation and the symmetry energy are key properties of low-energy nuclear physics that depend on fine details of the nuclear interaction. The equation of state around saturation is also an important anchor for extrapolations to higher densities and studies of neutron stars. Here we develop a unified statistical framework that uses realistic nuclear forces to link the theoretical modeling of finite nuclei and infinite nuclear matter. We construct fast and accurate emulators for nuclear-matter observables and employ an iterative history-matching approach to explore and reduce the enormous parameter domain of Δ-full chiral interactions. We perform rigorous uncertainty quantification and find that model calibration including O16 observables gives saturation predictions that are more precise than those that only use few-body data.
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| 7. |
- Kondo, Y., et al.
(author)
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First observation of 28 O
- 2023
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In: Nature. - 0028-0836 .- 1476-4687. ; 620:7976, s. 965-970
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Journal article (peer-reviewed)abstract
- Subjecting a physical system to extreme conditions is one of the means often used to obtain a better understanding and deeper insight into its organization and structure. In the case of the atomic nucleus, one such approach is to investigate isotopes that have very different neutron-to-proton (N/Z) ratios than in stable nuclei. Light, neutron-rich isotopes exhibit the most asymmetric N/Z ratios and those lying beyond the limits of binding, which undergo spontaneous neutron emission and exist only as very short-lived resonances (about 10−21s), provide the most stringent tests of modern nuclear-structure theories. Here we report on the first observation of 28O and 27O through their decay into 24O and four and three neutrons, respectively. The 28O nucleus is of particular interest as, with the Z = 8 and N = 20 magic numbers1,2, it is expected in the standard shell-model picture of nuclear structure to be one of a relatively small number of so-called ‘doubly magic’ nuclei. Both 27O and 28O were found to exist as narrow, low-lying resonances and their decay energies are compared here to the results of sophisticated theoretical modelling, including a large-scale shell-model calculation and a newly developed statistical approach. In both cases, the underlying nuclear interactions were derived from effective field theories of quantum chromodynamics. Finally, it is shown that the cross-section for the production of 28O from a 29F beam is consistent with it not exhibiting a closed N = 20 shell structure.
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| 8. |
- Koszorús, Agota, et al.
(author)
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Charge radii of exotic potassium isotopes challenge nuclear theory and the magic character of N = 32
- 2021
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In: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2481 .- 1745-2473. ; 17:4, s. 439-443
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Journal article (peer-reviewed)abstract
- Nuclear charge radii are sensitive probes of different aspects of the nucleon–nucleon interaction and the bulk properties of nuclear matter, providing a stringent test and challenge for nuclear theory. Experimental evidence suggested a new magic neutron number at N = 32 (refs. 1–3) in the calcium region, whereas the unexpectedly large increases in the charge radii4,5 open new questions about the evolution of nuclear size in neutron-rich systems. By combining the collinear resonance ionization spectroscopy method with β-decay detection, we were able to extend charge radii measurements of potassium isotopes beyond N = 32. Here we provide a charge radius measurement of 52K. It does not show a signature of magic behaviour at N = 32 in potassium. The results are interpreted with two state-of-the-art nuclear theories. The coupled cluster theory reproduces the odd–even variations in charge radii but not the notable increase beyond N = 28. This rise is well captured by Fayans nuclear density functional theory, which, however, overestimates the odd–even staggering effect in charge radii. These findings highlight our limited understanding of the nuclear size of neutron-rich systems, and expose problems that are present in some of the best current models of nuclear theory.
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| 9. |
- Yang, Chieh-Jen, 1977, et al.
(author)
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Calculations for nuclear matter and finite nuclei within and beyond energy-density-functional theories through interactions guided by effective field theory
- 2022
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In: Physical Review C. - 2469-9985 .- 2469-9993. ; 106:1
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Journal article (peer-reviewed)abstract
- We propose a novel idea to construct an effective interaction under energy-density-functional (EDF) theories which is adaptive to the enlargement of the model space. Guided by effective field theory principles, iterations of interactions as well as enlargements of the model space through particle-hole excitations are carried out for infinite nuclear matter and selected closed-shell nuclei (4He, 16O, 40Ca, 56Ni, and 100Sn) up to next-to-leading order. Our approach provides a new way for handling the nuclear matter and finite nuclei within the same scheme, with advantages from both EDF and ab initio approaches.
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