| 1. |
- Becker, K. S., et al.
(författare)
-
Ab initio symmetry-adapted emulator for studying emergent collectivity and clustering in nuclei
- 2023
-
Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 11
-
Tidskriftsartikel (refereegranskat)abstract
- We discuss emulators from the ab initio symmetry-adapted no-core shell-model framework for studying the formation of alpha clustering and collective properties without effective charges. We present a new type of an emulator, one that utilizes the eigenvector continuation technique but is based on the use of symplectic symmetry considerations. This is achieved by using physically relevant degrees of freedom, namely, the symmetry-adapted basis, which exploits the almost perfect symplectic symmetry in nuclei. Specifically, we study excitation energies, point-proton root-mean-square radii, along with electric quadrupole moments and transitions for 6Li and 12C. We show that the set of parameterizations of the chiral potential used to train the emulators has no significant effect on predictions of dominant nuclear features, such as shape and the associated symplectic symmetry, along with cluster formation, but slightly varies details that affect collective quadrupole moments, asymptotic normalization coefficients, and alpha partial widths up to a factor of two. This makes these types of emulators important for further constraining the nuclear force for high-precision nuclear structure and reaction observables.
|
|
| 2. |
- Ekström, Andreas, 1980, et al.
(författare)
-
What is ab initio in nuclear theory?
- 2023
-
Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 11
-
Forskningsöversikt (refereegranskat)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.
|
|
| 3. |
- Kondo, Y., et al.
(författare)
-
First observation of 28 O
- 2023
-
Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 620:7976, s. 965-970
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 4. |
- Miller, Sean, 1993, et al.
(författare)
-
Posterior predictive distributions of neutron-deuteron cross sections
- 2023
-
Ingår i: Physical Review C. - 2469-9993 .- 2469-9985. ; 107:1
-
Tidskriftsartikel (refereegranskat)abstract
- We quantify the posterior predictive distributions (PPDs) of elastic neutron-deuteron (nd) scattering cross sections using nucleon-nucleon (NN) interactions from chiral effective field theory (χEFT) up to and including next-to-next-to-next-to-leading order (N3LO). These PPDs quantify the spread in nd predictions due to the variability of the low-energy constants (LECs) inferred from NN scattering data. We use the wave-packet continuum discretization method to solve the Alt-Grassberger-Sandhas form of the Faddeev equations for elastic scattering. We draw 100 samples from the PPDs of nd cross sections up to 67 MeV in scattering energy, i.e., in the energy region where the effects of three-nucleon forces are expected to be small. We find that the uncertainty about NN LECs inferred from NN scattering data, when assuming uncorrelated errors, does not translate to significant uncertainty in the low-energy nd continuum. Based on our estimates, the uncertainty of nd predictions are dominated by the χEFT truncation error, at least below N3LO. At this order, the 90% credible interval of the PPD and the truncation error are comparable, although both are very small on an absolute scale.
|
|
| 5. |
- Sundh, Josefin, 1972-, et al.
(författare)
-
Risk and outcomes of COVID-19 in patients with oxygen-dependent chronic respiratory failure- a national cohort study.
- 2023
-
Ingår i: Respiratory medicine. - : Elsevier. - 1532-3064 .- 0954-6111. ; 218
-
Tidskriftsartikel (refereegranskat)abstract
- We aimed to evaluate cumulative occurrence and impact of COVID-19 in patients with chronic respiratory failure (CRF) treated with long-term oxygen therapy (LTOT).Data were obtained from the SCIFI-PEARL study on the entire Swedish population and on patients with oxygen-dependent CRF and no COVID-19 diagnosis before start of LTOT. Analyses were performed for three time periods; pre-alpha (Jan-Dec 2020), alpha (Jan-Mar 2021) and delta/omicron (Apr 2021-May 2022). Cumulative incidence of laboratory-verified COVID-19 was compared between patients with CRF and the general population. Risk factors for severe (hospitalised) to critical (intensive care, or death ≤30 days after infection) COVID-19, and the impact of COVID-19 on one-year mortality, were analysed using multivariable Cox regression.Cumulative incidence of COVID-19 was higher in patients with CRF than in the general population during the pre-alpha period (6.4%/4.9%, p=0.002), but less common during the alpha and delta/omicron periods (2.9%/3.8% and 7.8%/15.5%, p<0.0001 for both). The risk of severe/critical COVID-19 was much higher in CRF patients during all periods (4.9%/0.5%, 3.8%/0.2% and 15.5%/0.5%, p<0.0001 for all). Risk factors for COVID-19 infection in people with CRF were higher age, cardiovascular and renal disease, and COVID-19 was associated with increased one-year mortality following infection in the pre-alpha (HR 1.79; [95% CI] 1.27-2.53) and alpha periods (1.43; 1.03-1.99).Patients with CRF had higher risk of severe/critical COVID-19 than the general population. COVID-19 infection was associated with excess one-year mortality.
|
|
| 6. |
- Svensson, Isak, 1988, et al.
(författare)
-
Bayesian estimation of the low-energy constants up to fourth order in the nucleon-nucleon sector of chiral effective field theory
- 2023
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 107:1
-
Tidskriftsartikel (refereegranskat)abstract
- We use Bayesian methods and Hamiltonian Monte Carlo (HMC) sampling to infer the posterior probability density function (PDF) for the low-energy constants (LECs) up to next-to-next-to-next-to-leading order (N3LO) in a chiral effective field theory (χEFT) description of the nucleon-nucleon interaction. In a first step, we condition the inference on neutron-proton and proton-proton scattering data and account for uncorrelated χEFT truncation errors. We demonstrate how to successfully sample the 31-dimensional space of LECs at N3LO using a revised HMC inference protocol. In a second step we extend the analysis by means of importance sampling and an empirical determination of the neutron-neutron scattering length to infer the posterior PDF for the leading charge-dependent contact LEC in the S01 neutron-neutron interaction channel. While doing so we account for the χEFT truncation error via a conjugate prior. We use the resulting posterior PDF to sample the posterior predictive distributions for the effective range parameters in the S01 wave as well as the strengths of charge-symmetry breaking and charge-independence breaking. We conclude that empirical point-estimate results of isospin breaking in the S01 channel are consistent with the PDFs obtained in our Bayesian analysis and that, when accounting for χEFT truncation errors, one must go to next-to-next-to-leading order to confidently detect isospin breaking effects.
|
|
| 7. |
- Thim, Oliver, 1997, et al.
(författare)
-
Bayesian analysis of chiral effective field theory at leading order in a modified Weinberg power counting approach
- 2023
-
Ingår i: Physical Review C. - 2469-9993 .- 2469-9985. ; 108:5
-
Tidskriftsartikel (refereegranskat)abstract
- We present a Bayesian analysis of renormalization-group invariant nucleon-nucleon interactions at leading order in chiral effective field theory (χEFT) with momentum cutoffs in the range 400–4000 MeV. We use history matching to identify relevant regions in the parameter space of low-energy constants (LECs) and subsequently infer the posterior probability density of their values using Markov chain Monte Carlo. All posteriors are conditioned on experimental data for neutron-proton scattering observables and we estimate the χ EFT truncation error in an uncorrelated limit. We do not detect any significant cutoff dependence in the posterior predictive distributions for two-nucleon observables. For all cutoff values we find a multimodal LEC posterior with an insignificant mode harboring a bound 1S0 state. The 3P0 and 3P2 phase shifts emerging from the Bayesian analysis are less constrained and typically more repulsive compared to the results of a phase shift optimization. We expect that our inference will impact predictions for nuclei. This work demonstrates how to perform inference in the presence of limit-cycle-like behavior and spurious bound states, and lays the foundation for a Bayesian analysis of renormalization-group invariant χEFT interactions beyond leading order.
|
|
| 8. |
- Yang, Chieh-Jen, 1977, et al.
(författare)
-
The importance of few-nucleon forces in chiral effective field theory
- 2023
-
Ingår i: European Physical Journal A. - 1434-601X .- 1434-6001. ; 59:10
-
Tidskriftsartikel (refereegranskat)abstract
- We study the importance of few-nucleon forces in chiral effective field theory for describing many-nucleon systems. A combinatorial argument suggests that three-nucleon forces-which are conventionally regarded as next-to-next-to-leading order-should accompany the two-nucleon force already at leading order (LO) starting with mass number A≃ 10–20. We find that this promotion enables the first realistic description of the 16 O ground state based on a renormalization-group-invariant LO interaction. We also performed coupled-cluster calculations of the equation of state for symmetric nuclear matter and our results indicate that LO four-nucleon forces could play a crucial role for describing heavy-mass nuclei. The enhancement mechanism we found is very general and could be important also in other many-body problems.
|
|
