118974414
Low momentum shell model effective interactions with all-order core polarizations
An all-order summation of core-polarization diagrams using the low-momentum nucleon-nucleon interaction V{sub low-k} is presented. The summation is based on the Kirson-Babu-Brown (KBB) induced interaction approach in which the vertex functions are obtained self-consistently by solving a set of nonlinear coupled equations. It is found that the solution of these equations is simplified using V{sub low-k}, which is energy independent, and using the Green's functions in the particle-particle and particle-hole channels. We have applied this approach to the sd-shell effective interactions and find that the results we calculated to all orders by using the KBB summation technique are remarkably similar to those of second-order perturbation theory, the average differences being less than 10%.
119226065
Chiral three-nucleon forces and bound excited states in neutron-rich oxygen isotopes
We study the spectra of neutron-rich oxygen isotopes based on chiral two- and three-nucleon interactions. First, we benchmark our many-body approach by comparing ground-state energies to coupled-cluster results for the same two-nucleon interaction, with overall good agreement. We then calculate bound excited states in 21, 22, 23O , focusing on the role of three-nucleon forces, in the standard sd shell and an extended $ sdf_{7/2}p_{3/2}$ valence space. Chiral three-nucleon forces provide important one- and two-body contributions between valence neutrons. We find that both these contributions and an extended valence space are necessary to reproduce key signatures of novel shell evolution, such as the N = 14 magic number and the low-lying states in 21O and 23O , which are too compressed with two-nucleon interactions only. For the extended space calculations, this presents first work based on nuclear forces without adjustments. Future work is needed and open questions are discussed.
119225778
Tensor interaction constraints from beta decay recoil spin asymmetry of trapped atoms
We have measured the angular distribution of recoiling daughter nuclei emitted from the Gamow-Teller {beta} decay of spin-polarized {sup 80}Rb. The asymmetry of this distribution vanishes to lowest order in the standard model (SM) in pure Gamow-Teller decays, producing an observable very sensitive to new interactions. We measure the non-SM contribution to the asymmetry to be A{sub T}=0.015{+-}0.029 (stat) {+-}0.019 (syst), consistent with the SM prediction. We constrain higher-order SM corrections using the measured momentum dependence of the asymmetry, and their remaining uncertainty dominates the systematic error. Future progress in determining the weak magnetism term theoretically or experimentally would reduce the final errors. We describe the resulting constraints on fundamental four-Fermi tensor interactions.
56294645
Three-body forces and shell structure in calcium isotopes
Understanding and predicting the formation of shell structure from nuclear forces is a central challenge for nuclear physics. While the magic numbers N = 2, 8, 20 are generally well understood, N = 28 is the first standard magic number that is not reproduced in microscopic theories with two-nucleon forces. In this paper, we show that three-nucleon forces give rise to repulsive interactions between two valence neutrons that are key to explain 48Ca as a magic nucleus, with a high 2+ excitation energy and a concentrated magnetic dipole transition strength. The repulsive three-nucleon mechanism improves the agreement with experimental binding energies. Communicated by Professor Jacek Dobaczewski
7797374
First direct double-β decay Q-value measurement of 82Se in support of understanding the nature of the neutrino.
In anticipation of results from current and future double-β decay studies, we report a measurement resulting in a (82)Se double-β decay Q value of 2997.9(3) keV, an order of magnitude more precise than the currently accepted value. We also present preliminary results of a calculation of the (82)Se neutrinoless double-β decay nuclear matrix element that corrects in part for the small size of the shell model single-particle space. The results of this work are important for designing next generation double-β decay experiments and for the theoretical interpretations of their observations.
30767099
Microscopic restoration of proton-neutron mixed symmetry in weakly collective nuclei
Starting from the microscopic low-momentum nucleon-nucleon interaction V{sub lowk}, we present a systematic shell-model study of magnetic moments and magnetic dipole transition strengths of the basic low-energy one-quadrupole phonon excitations in nearly spherical nuclei. Studying in particular the even-even N=52 isotones from {sup 92}Zr to {sup 100}Cd, we find the predicted evolution of the predominantly proton-neutron nonsymmetric state reveals a restoration of collective proton-neutron mixed-symmetry structure near midshell. This provides a quantitative explanation for the existence of pronounced collective mixed-symmetry structures in weakly collective nuclei.
117812224
Reduced regulator dependence of neutron-matter predictions with perturbative chiral interactions
We calculate the energy per particle in infinite neutron matter perturbatively using chiral N3LO two-body potentials plus N2LO three-body forces. The cutoff dependence of the predictions is investigated by employing chiral interactions with different regulators. We find that the inclusion of three-nucleon forces, which are consistent with the applied two-nucleon interaction, leads to a strongly reduced regulator dependence of the results.
118621070
Density-dependent effective nucleon-nucleon interaction from chiral three-nucleon forces
We derive density-dependent corrections to the in-medium nucleon-nucleon interaction from the leading-order chiral three-nucleon force. To this order there are six distinct one-loop diagrams contributing to the in-medium nucleon-nucleon scattering T matrix. Analytic expressions are presented for each of these in both isospin-symmetric nuclear matter and nuclear matter with a small isospin asymmetry. The results are combined with the low-momentum nucleon-nucleon potential V low k to obtain an effective density-dependent interaction suitable for nuclear structure calculations. The in-medium interaction is decomposed into partial waves up to orbital angular momentum L = 2. Our results should be particularly useful in calculations where an exact treatment of the chiral three-nucleon force would otherwise be computationally prohibitive.
103944970
Nuclear thermodynamics from chiral low-momentum interactions
We investigate the thermodynamic equation of state of isospin-symmetric nuclear matter with microscopic nuclear forces derived within the framework of chiral effective field theory. Two- and three-body nuclear interactions constructed at low-resolution scales form the basis for a perturbative calculation of the finite-temperature equation of state. The nuclear force models and many-body methods are benchmarked against bulk properties of isospin-symmetric nuclear matter at zero temperature, which are found to be well reproduced when chiral nuclear interactions constructed at the lowest resolution scales are employed. The calculations are then extended to finite temperatures, where we focus on the liquid-gas phase transition and the associated critical point. The Maxwell construction is applied to construct the physical equation of state, and the value of the critical temperature is determined to be ${T}_{c}=17.2$\char21{}19.1 MeV, in good agreement with the value extracted from multifragmentation reactions of heavy ions.
117291846
Density-dependent nuclear interactions and the beta decay of 14C: chiral three-nucleon forces and Brown-Rho scaling
We study the role of density-dependent low-momentum nucleon-nucleon interactions in describing the anomalously long beta decay lifetime of 14C. We approach this problem both from the perspective of chiral effective field theory, in which genuine three-body forces generate an effective density-dependent two-body interaction, as well as from the perspective of Brown-Rho scaling, in which the masses and form factor cutoffs in one-boson-exchange interactions are modified in a dense nuclear medium due to the partial restoration of chiral symmetry. The beta decay transition of 14C to the ground state of 14N is calculated within the shell model using a model space consisting of two 0p-shell holes within a closed 16O core. The effective 0p-shell interaction is calculated up to second order in perturbation theory with single-particle energies extracted from experiment. We find that both three-nucleon forces and Brown-Rho scaling medium modifications give qualitatively similar results not only for the ground state to ground state Gamow-Teller transition but also for Gamow-Teller transitions from excited states of 14C to the ground state of 14N. In this way, it is observed that at a low-momentum scale of V_(low-k) = 2.1 fm-1, medium-modifications of the nuclear force play an essential role in increasing the lifetime of 14C from a few minutes to an archaeologically long one of 5730 years.
59421221
Chiral nuclear dynamics with three-body forces ☆
We review recent progress in implementing high-precision chiral two- and three-body forces in nuclear many-body systems beyond light nuclei. We begin with applications to finite nuclei, which we study through the nuclear shell model and self-consistent mean field theory. We then turn our attention to infinite nuclear matter treated within the framework of Landau’s theory of normal Fermi liquids.