Ground-state correlations within a nonperturbative approach

Abstract

The contribution of the two-phonon configurations to the ground state of 4 He and 16 O is evaluated nonperturbatively using a Hartree-Fock basis within an equation-of-motion phonon method using a nucleonnucleon optimized chiral potential. Convergence properties of energies and root-mean-square radii versus the harmonic oscillator frequency and space dimensions are investigated. The comparison with the second-order perturbation theory calculations shows that the higher-order terms have an appreciable repulsive effect and yield too-small binding energies and nuclear radii. It is argued that four-phonon configurations, through their strong coupling to two phonons, may provide most of the attractive contribution necessary for filling the gap between theoretical and experimental quantities. Possible strategies for accomplishing such a challenging task are discussed.

Microscopic multiphonon approach to spectroscopy in the neutron-rich oxygen region

“…These forces are devised so as to reproduce the bulk properties at the HF(B) level, which is not our case. In fact, the HF calculation using the optimized NNLO opt yields only halfbinding energy [41]. The good agreement achieved in the mentioned RPA approaches suggests that the 2 + state has a much larger proton content than the one obtained here.…”

“…It was implemented numerically to describe the dipole response in heavy, neutron rich, nuclei [38][39][40], to study the full spectrum as well as the dipole response of the neutron rich 20 O [37], and to investigate the ground state correlations [41].…”

The equation of motion phonon method and its application in the neutron rich oxygen region

“…The equation of motion phonon method (EMPM) has been also used to study the nuclei in this region. The method was first formulated for even-even nuclei in the particle-hole (p-h) scheme [26][27][28] and, then, in terms of Hartree-Fock-Bogoliubov (HFB) quasiparticles (qp) [29]. It derives a set of equations yielding a basis of orthonormal multiphonon states, built of phonons obtained in Tamm-Dancoff approximation (TDA), and, then, solves the full eigenvalue problem in the space spanned by such a basis.…”

“…It takes the Pauli principle into full account and does not rely on any approximation. It has been adopted to study spectra and dipole responses of light and heavy even-even nuclei [30][31][32][33].…”

“…More recently it has been also extended to odd nuclei [34][35][36]. An orthonormal basis of states composed of a va-lence particle coupled to n-phonon states (n = 0, 1, 2, .…”