Search

We present a novel framework to decompose three-nucleon forces in a momentum-space partial-wave basis. The new approach is computationally much more efficient than previous methods and opens the way to ab initio studies of few-nucleon scattering processes, nuclei, and nuclear matter based on higher-order chiral three-nucleon forces. We use the new framework to calculate matrix elements of chiral three-nucleon forces at next-to-next-to-leading-order and next-to-next-to-next-to-leading-order in large basis spaces and carry out benchmark calculations for neutron matter and symmetric nuclear matter. We also study the size of the individual three-nucleon-force contributions for ³H. For nonlocal regulators, we find that the subleading terms, which have been neglected in most calculations so far, provide important contributions. All matrix elements are calculated and stored in a user-friendly way, such that values of low-energy constants as well as the form of regulator functions can be chosen freely. [ABSTRACT FROM AUTHOR]

We present the first results for the neutron matter equation of state (EOS) using nucleon-nucleon and three-nucleon chiral effective field theory interactions that are consistently evolved in the framework of the similarity renormalization group (SRG). The dependence of the EOS on the SRG resolution scale is greatly reduced when induced three-nucleon forces (3NF) are included, and the residual variation, which in part is from missing induced four-body interactions, is comparable to estimated many-body perturbation theory truncation errors. The relative growth with decreasing resolution of the 3NF contributions to the energy per neutron is of natural size, but it accelerates at the lowest resolutions where strong renormalization of the long-range 3NF matrix elements is also observed. [ABSTRACT FROM AUTHOR]

A framework to evolve three-nucleon (3N) forces in a plane-wave basis with the similarity renormalizution group (SRG) is presented and applied to consistent interactions derived from chiral effective field theory at next-to-next-to-leading order. We demonstrate the unitarity of the SRG transformation, show the decoupling of low and high momenta, and present the first investigation of universality in chiral 3N forces at low resolution scales. The momentum-space-evolved 3N forces are consistent and can be directly combined with the standard SRG-evolved two-nucleon (NN) interactions for ab initio calculations of nuclear structure and reactions. [ABSTRACT FROM AUTHOR]

We present nuclear matter calculations based on low-momentum interactions derived from chiral effective field theory potentials. The current calculations use an improved treatment of the three-nucleon force (3NF) contribution that includes a corrected combinatorial factor beyond Hartree-Fock that was omitted in previous nuclear matter calculations. We find realistic saturation properties using parameters fit only to few-body data, but with larger uncertainty estimates from cutoff dependence and the 3NF parametrization than in previous calculations. [ABSTRACT FROM AUTHOR]

We study the energy of an impurity (polaron) that interacts strongly in a sea of fermions when the effective range of the impurity-fermion interaction becomes important, thereby mapping the Fermi polaron of condensed matter physics and ultracold atoms to strongly interacting neutrons. We present quantum Monte Carlo results for this neutron polaron, and compare these with effective field theory calculations that also include contributions beyond the effective range. We show that state-of-the-art nuclear density functionals vary substantially and generally underestimate the neutron polaron energy. Our results thus provide constraints for adjusting the time-odd components of nuclear density functionals to better characterize polarized systems. [ABSTRACT FROM AUTHOR]

The neutron-matter equation of state constrains the properties of many physical systems over a wide density range and can be studied systematically using chiral effective field theory (EFT). In chiral EFT, all many-body forces among neutrons are predicted to next-to-next-to-next-to-leading order (N³LO). We present details and additional results of the first complete N³LO calculation of the neutron-matter energy, which includes the subleading three-nucleon as well as the leading four-nucleon forces, and provides theoretical uncertainties. In addition, we discuss the impact of our results for astrophysics: for the supernova equation of state, the symmetry energy and its density derivative, and for the structure of neutron stars. Finally, we give a first estimate for the size of the N³LO many-body contributions to the energy of symmetric nuclear matter, which shows that their inclusion will be important in nuclear structure calculations. [ABSTRACT FROM AUTHOR]

Renormalization-group (RG) methods used to soften Hamiltonians for nuclear many-body calculations change the effective resolution of the interaction. For nucleón knockout processes, these RG transformations leave cross sections invariant, but initial-state wave functions, interaction currents, and final-state interactions are individually altered. This has implications for the factorization of nuclear structure and reactions. We use deuteron electrodisintegration as a controlled laboratory for studying how structure and reaction components are modified under RG evolution, without the complication of three-body forces or currents. The dependence of these changes on kinematics is explored. [ABSTRACT FROM AUTHOR]

We present details of the derivation of local chiral effective field theory interactions to next-to-next-to-leading order and show results for nucleon-nucleon phase shifts and deuteron properties for these potentials. We then perform systematic auxiliary-field diffusion Monte Carlo calculations for neutron matter based on the developed local chiral potentials at different orders. This includes studies of the effects of the spectral-function regularization and of the local regulators. For all orders, we compare the quantum Monte Carlo results with perturbative many-body calculations and find excellent agreement for low cutoffs. [ABSTRACT FROM AUTHOR]

The symmetry energy contribution to the nuclear equation of state impacts various phenomena in nuclear astrophysics, nuclear structure, and nuclear reactions. Its determination is a key objective of contemporary nuclear physics, with consequences for the understanding of dense matter within neutron stars. We examine the results of laboratory experiments that have provided initial constraints on the nuclear symmetry energy and on its density dependence at and somewhat below normal nuclear matter density. Even though some of these constraints have been derived from properties of nuclei while others have been derived from the nuclear response to electroweak and hadronic probes, within experimental uncertainties-they are consistent with each other. We also examine the most frequently used theoretical models that predict the symmetry energy and its slope parameter. By comparing existing constraints on the symmetry pressure to theories, we demonstrate how contributions of three-body forces, which are essential ingredients in neutron matter models, can be determined. [ABSTRACT FROM AUTHOR]