Regulator functions applied to two-and three-nucleon forces are a necessary ingredient in manybody calculations based on chiral effective field theory interactions. These interactions have been developed recently with a variety of different cutoff forms, including regulating both the momentum transfer (local) and the relative momentum (nonlocal). While in principle any regulator that suppresses high momentum modes can be employed, in practice artifacts are inevitable in current power counting schemes. Artifacts from particular regulators may cause significant distortions of the physics or may affect many-body convergence rates, so understanding their nature is important. Here we characterize the differences between cutoff effects using uniform matter at Hartree-Fock and second-order in the interaction as a testbed. This provides a clean laboratory to isolate phase-space effects of various regulators on both two-and three-nucleon interactions. We test the normalordering approximation for three-nucleon forces in nuclear matter and find that the relative size of the residual 3N contributions is sensitive to the employed regularization scheme.

Background: Energy density functional methods provide a generic framework to compute properties of atomic nuclei starting from models of nuclear potentials and the rules of quantum mechanics. Until now, the overwhelming majority of functionals have been constructed either from empirical nuclear potentials such as the Skyrme or Gogny forces, or from systematic gradient-like expansions in the spirit of the density functional theory for atoms.Purpose: We seek to obtain a usable form of the nuclear energy density functional that is rooted in the modern theory of nuclear forces. We thus consider a functional obtained from the density matrix expansion of local nuclear potentials from chiral effective field theory. We propose a parametrization of this functional carefully calibrated and validated on selected ground-state properties that is suitable for large-scale calculations of nuclear properties.Methods: Our energy functional comprises two main components. The first component is a non-local functional of the density and corresponds to the direct part (Hartree term) of the expectation value of local chiral potentials on a Slater determinant. Contributions to the mean field and the energy of this term are computed by expanding the spatial, finite-range components of the chiral potential onto Gaussian functions. The second component is a local functional of the density and is obtained by applying the density matrix expansion to the exchange part (Fock term) of the expectation value of the local chiral potential. We apply the unedf2 optimization protocol to determine the coupling constants of this energy functional. Results:We obtain a set of microscopically-constrained functionals for local chiral potentials from leading-order up to next-to-next-to-leading order with and without three-body forces and contributions from ∆ excitations. These functionals are validated on the calculation of nuclear and neutron matter, nuclear mass tables, singleparticle shell structure in closed-shell nuclei and the fission barrier of 240 Pu. Quantitatively, they perform noticeable better than the more phenomenological Skyrme functionals. Conclusions:The inclusion of higher-order terms in the chiral perturbation expansion seems to produce a systematic improvement in predicting nuclear binding energies while the impact on other observables is not really significant. This result is especially promising since all the fits have been performed at the single-reference level of the energy density functional approach, where important collective correlations such as center-of-mass correction, rotational correction or zero-point vibrational energies have not been taken into account yet. * navarrop@ohio.edu † schunk1@llnl.gov ‡ dyhdalo.2@osu.edu § furnstahl.1@osu.edu ¶ bogner@nscl.msu.edu potentials. In light nuclei, the no-core shell model [3] or Quantum Monte-Carlo methods [4] are popular examples of such direct approaches; in heavier nuclei, alternative methods such as the coupled-cluster [5] or inmedium similarity renormalization group [6] can pro...

We apply the density matrix expansion (DME) at Hartree-Fock level with long-range chiral effective field theory interactions defined in coordinate space up to next-to-next-to-leading order. We consider chiral potentials both with and without explicit Delta isobars. The challenging algebra associated with applying the DME to three-nucleon forces is tamed using a new organization scheme, which will also facilitate generalizations. We include local regulators on the interactions to mitigate the effects of singular potentials on the DME couplings and simplify the optimization of generalized Skyrme-like functionals. *

Modern softened nucleon-nucleon interactions are well-suited for perturbative many-body calculations, but a many-body power counting scheme is lacking. Estimates of diagrammatic contributions at finite density are important ingredients in such a scheme. Here we show how to make quantitative estimates of the particle-particle and hole-hole channel in uniform nuclear matter for soft interactions. We also use estimates to assess the role of normal-ordered three-body forces for a pure contact interaction. *