Properties of⁴He and⁶Li with improved chiral EFT interactions

Abstract

Abstract. We present recent results for 4 He and 6 Li obtained with improved NN interactions derived from chiral effective field theory up to N 4 LO. The many-body calculations are performed order-by-order in the chiral expansion. At N 3 LO and N 4 LO additional renormalization using the Similarity Renormalization Group is adopted to improve numerical convergence of the many-body calculations. We discuss results for the ground state energies, as well as the magnetic moment and the low-lying spectrum of 6 Li. Nuclear potential from chiral EFTChiral effective field theory (EFT) allows one to derive nuclear forces (and corresponding electoweak currents) in a systematical way [1]. In particular, the leading order (LO) and next-to-leading order (NLO) contributions to the interaction are given solely by nucleon-nucleon (NN) operators while three-nucleon forces (3NFs) appear first at next-to-next-to-leading order (N 2 LO) [2] in the chiral expansion. Four-nucleon forces are even more suppressed and start contributing at N 3 LO. The chiral power counting thus provides a natural explanation of the observed hierarchy of nuclear forces.In Refs. [3, 4] a new generation of chiral EFT NN potentials up to N 4 LO was developed, using local regulators for the long-range terms and with reduced finite-cutoff artefacts by employing a novel ultraviolet regularization scheme; in addition, a procedure to estimate the theoretical uncertainties due to the truncation of the chiral expansion was proposed (see also [5]). Here we present results for 4 He and 6 Li obtained with these improved chiral NN potentials using a regulator of R = 1.0 fm [6]. a

Theoretical uncertainties of the elastic nucleon-deuteron scattering observables

“…[29,40] was found for Nd elastic scattering [30] and for various electroweak processes [31]. Also the nuclear structure calculations confirmed this observation [41,42].…”

Semilocal momentum-space regularized chiral two-nucleon potentials up to fifth order

“…In combination with the algorithm for quantification of truncation errors formulated in Ref. [6], that exploits the available information on the chiral expansion for an observable of interest to estimate the size of neglected higher-order terms without relying on cutoff variation, the EKM NN potentials were found to yield promising results for nucleon-deuteron scattering and the properties of light nuclei [21,22], selected electroweak processes involving two-and three-nucleon systems [23,24] and nuclear matter properties [25], see also Ref. [26] for a recent application to derive an optical potential for describing elastic proton-nucleus scattering.…”

Effective operators in two-nucleon systems

“…In particular, there is a dramatic slowing of the convergence rates at N 3 LO as seen in panel (c) compared to panels (a) and (b). The dependence of the convergence rates on the LENPIC chiral orders is also revealed in many-body observables where slower convergence leads to larger extrapolation uncertainties [12][13][14].…”

“…For a sufficiently large N max , some observables are seen to converge in very light nuclei for interactions which do not couple strongly to high momentum states and when computational resources are sufficient. For example, using a chiral N 2 LO N N interaction [10,11], the ground state (gs) energy of 6 Li has been calculated [12][13][14] in a sequence of HO basis spaces. With extrapolation to the complete basis, the result is −31.0(2) MeV [14].…”

“…We adopt N N interactions from chiral Effective Field Theory (EFT) and we include the Coulomb interaction between proton pairs in the Hamiltonian. Specifically, we employ the N N interactions of the Low Energy Nuclear Physics International Collaboration (LENPIC) [10][11][12][13][14] which have been developed for each chiral order up through N 4 LO. These LENPIC interactions employ a semilocal coordinate-space regulator and we select the interactions with the regulator range R = 1.0 fm [13,14].…”