Quasiparticle Random Phase Approximation with Interactions from the Similarity Renormalization Group

TL;DR

This paper introduces a consistent QRPA framework using SRG-evolved realistic interactions, enabling accurate nuclear response calculations without empirical corrections, and explores the impact of SRG parameters on calcium isotopes.

Contribution

The work develops a fully consistent QRPA approach with SRG interactions, including a density-dependent approximation for 3N effects, and applies it to study nuclear responses across calcium isotopes.

Findings

Good decoupling of spurious strength without empirical corrections

Response properties depend on SRG parameter $mbda$

Spin-orbit splittings indicate need for 3N interaction terms

Abstract

We have developed a fully consistent framework for calculations in the Quasiparticle Random Phase Approximation (QRPA) with $NN$ interactions from the Similarity Renormalization Group (SRG) and other unitary transformations of realistic interactions. The consistency of our calculations, which use the same Hamiltonian to determine the Hartree-Fock-Bogoliubov (HFB) ground states and the residual interaction for QRPA, guarantees an excellent decoupling of spurious strength, without the need for empirical corrections. While work is under way to include SRG-evolved 3N interactions, we presently account for some 3N effects by means of a linearly density-dependent interaction, whose strength is adjusted to reproduce the charge radii of closed-shell nuclei across the whole nuclear chart. As a first application, we perform a survey of the monopole, dipole, and quadrupole response of the calcium isotopic chain and of the underlying single-particle spectra, focusing on how their properties depend on the SRG parameter $\lambda$. Unrealistic spin-orbit splittings suggest that spin-orbit terms from the 3N interaction are called for. Nevertheless, our general findings are comparable to results from phenomenological QRPA calculations using Skyrme or Gogny energy density functionals. Potentially interesting phenomena related to low-lying strength warrant more systematic investigations in the future.