Search

We employ a variety of ab initio methods, including Faddeev-Yakubovsky equations, no-core configuration interaction approach, coupled-cluster theory, and in-medium similarity renormalization group, to perform a comprehensive analysis of the nucleon-deuteron elastic and breakup reactions and selected properties of light and medium-mass nuclei up to 48Ca using the recently constructed semilocal coordinate-space regularized chiral nucleon-nucleon potentials. We compare the results with those based on selected phenomenological and chiral EFT two-nucleon potentials, discuss the convergence pattern of the chiral expansion, and estimate the achievable theoretical accuracy at various chiral orders using an approach to quantify truncation errors of the chiral expansion without relying on cutoff variation. We also address the robustness of this method and explore alternative ways to estimate the theoretical uncertainty from the truncation of the chiral expansion. [ABSTRACT FROM AUTHOR]

Background: The exotic 9He nucleus, which presents one of the most extreme neutron-to-proton ratios, belongs to the N=7 isotonic chain famous for the phenomenon of ground-state parity inversion with decreasing number of protons. Consequently, it would be expected to have an unnatural (positive) parity ground state similar to 11Be and 10Li. Despite many experimental and theoretical investigations, its structure remains uncertain. Apart from the fact that it is unbound, other properties including the spin and parity of its ground state, and the very existence of additional low-lying resonances are still a matter of debate. Purpose: In this work, we study the properties of 9He by analyzing the n+8He continuum in the context of the ab initio no-core shell model with continuum (NCSMC) formalism with chiral nucleon-nucleon interactions as the only input. Methods: The NCSMC is a state-of-the-art approach for the ab initio description of light nuclei. With its capability to predict properties of bound states, resonances, and scattering states in a unified framework, the method is particularly well suited for the study of unbound nuclei such as 9He. Results: Our analysis produces an unbound 9He nucleus. Two resonant states are found at the energies of ~1 and ~3.5 MeV, respectively, above the n+8He breakup threshold. The first state has a spin-parity assignment of Jp=1/2- and can be associated with the ground state of 9He, while the second, broader state has a spin parity of 3/2-. No resonance is found in the 1/2+ channel, only a very weak attraction. Conclusions: We find that the 9He ground-state resonance has a negative parity and thus breaks the parity-inversion mechanism found in the 11Be and 10Li nuclei of the same N=7 isotonic chain. [ABSTRACT FROM AUTHOR]

The weakly bound exotic 11Be nucleus, famous for its ground-state parity inversion and distinct n+10Be halo structure, is investigated from first principles using chiral two- and three-nucleon forces. An explicit treatment of continuum effects is found to be indispensable. We study the sensitivity of the 11Be spectrum to the details of the three-nucleon force and demonstrate that only certain chiral interactions are capable of reproducing the parity inversion. With such interactions, the extremely large E1 transition between the bound states is reproduced. We compare our photodisintegration calculations to conflicting experimental data and predict a distinct dip around the 3/2-1 resonance energy. Finally, we predict low-lying 3/2+ and 9/2+ resonances that are not or not sufficiently measured in experiments. [ABSTRACT FROM AUTHOR]

We apply improved nucleon-nucleon potentials up to fifth order in chiral effective field theory, along with a new analysis of the theoretical truncation errors to study nucleon-deuteron (Nd) scattering and selected low-energy observables in ³H,4He, and 6Li. Calculations beyond second order differ from experiment well outside the range of quantified uncertainties, providing truly unambiguous evidence for missing three-nucleon forces within the employed framework. The sizes of the required three-nucleon-force contributions agree well with expectations based on Weinberg's power counting. We identify the energy range in elastic Nd scattering best suited to study three-nucleon-force effects and estimate the achievable accuracy of theoretical predictions for various observables. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine countermovement vertical jump performance among female athletes who rely heavily on vertical jump performance within their given sport. Forty-five female athletes representing 3 teams (basketball, volleyball, and beach volleyball) competing at the NCAA Division I level completed 2 maximal effort countermovement jumps (CMJ) using a portable force platform. A 1-way analysis of variance was used to compare groups across each variable. Statistically significant differences were found between the groups regarding propulsive duration and time to takeoff with basketball showing the shortest time and beach volleyball having the longest times (p, 0.05). In addition, differences were seen in countermovement depth and mean propulsive force between the groups with basketball displaying the smallest countermovement and highest force (p, 0.05). No differences were seen in jump height and reactive strength index modified. Greater force and shorter durations in basketball athletes versus the low force and long durations in the beach volleyball athletes suggest that sporting backgrounds play a large role in how the CMJ is performed. This information can aid strength and conditioning practitioners in the design of training programs that are sport specific to the strategies used by the athlete. [ABSTRACT FROM AUTHOR]

We investigate selected static and transition properties of 12C using ab initio no-core shell model (NCSM) methods with chiral two- and three-nucleon interactions. We adopt the similarity renormalization group (SRG) to assist convergence including up to three-nucleon (3 AO contributions. We examine the dependencies of the l2C observables on the SRG evolution scale and on the model-space parameters. We obtain nearly converged low-lying excitation spectra. We compare results of the full NCSM with the importance truncated NCSM in large model spaces for benchmarking purposes. We highlight the effects of the chiral 3N interaction on several spectroscopic observables. The agreement of some observables with experiment is improved significantly by the inclusion of 3N interactions, e.g., the B(M1) from the first Jπ T = 1+1 state to the ground state. However, in some cases the agreement deteriorates, e.g., for the excitation energy of the first l + 0 state, leaving room for improved next-generation chiral Hamiltonians. [ABSTRACT FROM AUTHOR]

We formulate the in-medium similarity renormalization group (IM-SRG) for open-shell nuclei using a multireference formalism based on a generalized Wick theorem introduced in quantum chemistry. The resulting multireference IM-SRG (MR-IM-SRG) is used to perform the first ab initio study of all even oxygen isotopes with chiral nucleon-nucleon and three-nucleon interactions, from the proton to the neutron drip lines. We obtain an excellent reproduction of experimental ground-state energies with quantified uncertainties, which is validated by results from the importance-truncated no-core shell model and the coupled cluster method. The agreement between conceptually different many-body approaches and experiment highlights the predictive power of current chiral two- and three-nucleon interactions, and establishes the MR-IM-SRG as a promising new tool for ab initio calculations of medium-mass nuclei far from shell closures. [ABSTRACT FROM AUTHOR]

We present the first ab initio coupled-cluster calculations of medium-mass nuclei with explicit chiral three-nucleon (3N) interactions. Using a spherical formulation of coupled cluster with singles and doubles excitations including explicit 3N contributions, we study ground states of 16,24O, 40,48Ca, and 56Ni. We employ chiral nucleon-nucleon (NN) plus 3N interactions softened through a similarity renormalization group (SRG) transformation at the three-body level. We investigate the impact of all truncations and quantify the resulting uncertainties--this includes the contributions from triple excitations, the truncation of the set of three-body matrix elements, and the omission of SRG-induced four-body interactions. Furthermore, we assess the quality of a normal-ordering approximation of the 3N interaction beyond light nuclei. Our study points towards the predictive power of chiral Hamiltonians in the medium-mass regime. [ABSTRACT FROM AUTHOR]

Introduction: Candidemia causes high mortality and is occuring at increasing rate in intensive care units (ICUs). (1,3)- β-D-glucan (BDG) testing is recommended in neutropenic patients. However the usefulness of BDG in ICUs is unclear. Methodology: This study was conducted to compare the diagnostic value of Candida score (CS), colonization index (CI), serum BDG detection, and routine laboratory parameters in ICU patients. Characteristics and laboratory data of 83 patients (15 patients with candidemia and 68 patients without candidemia) were evaluated. Results: Median serum BDG was significantly higher in the candidemia group (129 pg/mL vs. 36 pg/mL, p < 0.001). BDG assay with standard cut-off value ≥ of 80 pg/mL had 93.33% sensitivity and 64.18% specificity (Areas under the ROC curve (AUC): 0.788). This study concluded that the optimal cut-off value for BDG assay was 112 pg/mL with sensitivity of 86.67% and specificity of 82.09% (AUC: 0.844). C-reactive protein (CRP) with optimal cut-off value ≥ 85 mg/L and BDG ≥ 80 pg/mL had the highest AUC (0.862, 95% CI: 0.768 - 0.928) with sensitivity 93.33% and specificity 79.1%. Conclusions: Predicting candidemia is essential in critically ill patients who are at high risk and have high mortality rates. The results of this study suggest that BDG testing is useful for predicting candidemia in ICU. However, BDG combined with CRP may be a stronger predictor for candidemia. [ABSTRACT FROM AUTHOR]

Background: The nuclear optical potential is a successful tool for the study of nucleon-nucleus elastic scattering and its use has been further extended to inelastic scattering and other nuclear reactions. The nuclear density of the target nucleus is a fundamental ingredient in the construction of the optical potential and thus plays an important role in the description of the scattering process. Purpose: In this paper we derive a microscopic optical potential for intermediate energies using ab initio translationally invariant nonlocal one-body nuclear densities computed within the no-core shell model (NCSM) approach utilizing two- and three-nucleon chiral interactions as the only input. Methods: The optical potential is derived at first order within the spectator expansion of the nonrelativistic multiple scattering theory by adopting the impulse approximation. Nonlocal nuclear densities are derived from the NCSM one-body densities calculated in the second quantization. The translational invariance is generated by exactly removing the spurious center-of-mass (COM) component from the NCSM eigenstates. Results: The ground-state local and nonlocal densities of 4,6,8He, 12C, and 16O are calculated and applied to optical potential construction. The differential cross sections and the analyzing powers for the elastic proton scattering off these nuclei are then calculated for different values of the incident proton energy. The impact of nonlocality and the COM removal is discussed. Conclusions: The use of nonlocal densities has a substantial impact on the differential cross sections and improves agreement with experiment in comparison to results generated with the local densities especially for light nuclei. For the halo nuclei 6He and 8He, the results for the differential cross section are in a reasonable agreement with the data although a more sophisticated model for the optical potential is required to properly describe the analyzing powers. [ABSTRACT FROM AUTHOR]

We extend the recently proposed ab initio no-core shell model with continuum to include three-nucleon (3N) interactions beyond the few-body domain. The extended approach allows for the assessment of effects of continuum degrees of freedom as well as of the 3N force in ab initio calculations of structure and reaction observables of p- and lower-sd-shell nuclei. As a first application we concentrate on energy levels of the 9Be system for which all excited states lie above the n-Be8 threshold. For all energy levels, the inclusion of the continuum significantly improves the agreement with experiment, which was an issue in standard no-core shell model calculations. Furthermore, we find the proper treatment of the continuum indispensable for reliable statements about the quality of the adopted 3N interaction from chiral effective field theory. In particular, we find the ½+ resonance energy, which is of astrophysical interest, in good agreement with experiment. [ABSTRACT FROM AUTHOR]

We present the first ab initio calculations for p-shell single-A hypemuclei. For the solution of the manybaryon problem, we develop two variants of the no-core shell model with explicit A and Σ+,Σ0,Σ- hyperons including A-Σ conversion, optionally supplemented by a similarity renormalization group transformation to accelerate model-space convergence. In addition to state-of-the-art chiral two- and three-nucleon interactions, we use leading-order chiral hyperon-nucleon interactions and a recent mesonexchange hyperon-nucleon interaction. We validate the approach for 5-shell hypemuclei and apply it to p-shell hypemuclei, in particular to 7ΛLi, 9ΛBe, and 13ΛC. We show that the chiral hyperon-nucleon interactions provide ground-state and excitation energies that generally agree with experiment within the cutoff dependence. At the same time we demonstrate that hypemuclear spectroscopy provides tight constraints on the hyperon-nucleon interactions. [ABSTRACT FROM AUTHOR]

We use the newly developed multireference in-medium similarity renormalization group to study all even isotopes of the calcium and nickel isotopic chains, based on two- plus three-nucleon interactions derived from chiral effective field theory. We present results for ground-state and two-neutron separation energies and quantify their theoretical uncertainties. At shell closures, we find excellent agreement with coupled-cluster results obtained with the same Hamiltonians. Our results confirm the importance of chiral 3N interactions to obtain a correct reproduction of experimental energy trends, and their subtle impact in neutron-rich Ca and Ni isotopes. At the same time, we uncover and discuss deficiencies of the input Hamiltonians which need to be addressed by the next generation of chiral interactions. [ABSTRACT FROM AUTHOR]

We extend the ab initio no-core shell model/resonating-group method to include three-nucleon (3N) interactions for the description of nucleon-nucleus collisions. We outline the formalism, give algebraic expressions for the 3N-force integration kernels, and discuss computational aspects of two alternative implementations. The extended theoretical framework is then applied to nucleon-4He elastic scattering using similarity-renormalization-group (SRG)-evolved nucleon-nucleon plus 3N potentials derived from chiral effective field theory. We analyze the convergence properties of the calculated phase shifts and explore their dependence upon the SRG evolution parameter. We include up to six excited states of the 4He target and find significant effects from the inclusion of the chiral 3N force, e.g., it enhances the spin-orbit splitting between the 3/2-and 1/2- resonances and leads to an improved agreement with the phase shifts obtained from an accurate R-matrix analysis of the five-nucleon experimental data. We find remarkably good agreement with measured differential cross sections at various energies below the d-3H threshold, while analyzing powers manifest larger deviations from experiment for certain energies and angles. [ABSTRACT FROM AUTHOR]

How does nature hold together protons and neutrons to form the wide variety of complex nuclei in the Universe? Describing many-nucleon systems from the fundamental theory of quantum chromodynamics has been the greatest challenge in answering this question. The chiral effective field theory description of the nuclear force now makes this possible but requires certain parameters that are not uniquely determined. Defining the nuclear force needs identification of observables sensitive to the different parametrizations. From a measurement of proton elastic scattering on ^{10}C at TRIUMF and ab initio nuclear reaction calculations, we show that the shape and magnitude of the measured differential cross section is strongly sensitive to the nuclear force prescription.

The weakly bound exotic ^{11}Be nucleus, famous for its ground-state parity inversion and distinct n+^{10}Be halo structure, is investigated from first principles using chiral two- and three-nucleon forces. An explicit treatment of continuum effects is found to be indispensable. We study the sensitivity of the ^{11}Be spectrum to the details of the three-nucleon force and demonstrate that only certain chiral interactions are capable of reproducing the parity inversion. With such interactions, the extremely large E1 transition between the bound states is reproduced. We compare our photodisintegration calculations to conflicting experimental data and predict a distinct dip around the 3/2&#95;{1}^{-} resonance energy. Finally, we predict low-lying 3/2^{+} and 9/2^{+} resonances that are not or not sufficiently measured in experiments.

We present first ab initio no-core shell model (NCSM) calculations using similarity renormalization group (SRG) transformed chiral two-nucleon (NN) plus three-nucleon (3N) interactions for nuclei throughout the p-shell, particularly (12)C and (16)O. By introducing an adaptive importance truncation for the NCSM model space and an efficient JT-coupling scheme for the 3N matrix elements, we are able to surpass previous NCSM studies including 3N interactions. We present ground and excited states in (12)C and (16)O for model spaces up to N(max) = 12 including full 3N interactions. We analyze the contributions of induced and initial 3N interactions and probe induced 4N terms through the sensitivity of the energies on the SRG flow parameter. Unlike for light p-shell nuclei, SRG-induced 4N contributions originating from the long-range two-pion terms of the chiral 3N interaction are sizable in (12)C and (16)O.