Comment on "Pygmy dipole response of proton-rich argon nuclei in random-phase approximation and no-core shell model"

TL;DR

This paper critiques a recent study on low-energy dipole excitations in proton-rich argon nuclei, emphasizing the need for consistent methodology and validation against experimental data before claiming new exotic excitation modes.

Contribution

It highlights inconsistencies in previous research and stresses the importance of validating theoretical models with experimental data prior to exploring exotic nuclear excitations.

Findings

Identifies inconsistency with previous UCOM-RPA studies.

Questions the resonance-like nature of the low-lying state in $^{32}$Ar.

Emphasizes the need for experimental validation of models.

Abstract

In a recent article by C. Barbieri, E. Caurier, K. Langanke, and G. Mart\'inez-Pinedo \cite{Bar.08}, low-energy dipole excitations were studied in proton-rich $^{32,34}$Ar with random-phase approximation (RPA) and no-core shell model (NCSM) using correlated realistic nucleon-nucleon interactions obtained by the unitary correlation operator method (UCOM) \cite{Fel.98}. The main objective of this Comment is to argue that the article \cite{Bar.08} contains an inconsistency with respect to previous study of excitations in the same UCOM-RPA framework using identical correlated Argonne V18 interaction \cite{Paa.06}, it does not provide any evidence that the low-lying state declared as pygmy dipole resonance in $^{32}$Ar indeed has the resonance-like structure, and that prior to studying exotic modes of excitation away from the valley of stability one should ensure that the model provides reliable description of available experimental data on nuclear ground state properties and excitations in nuclei. Although the authors aimed at testing the UCOM based theory at the proton drip line, available experimental data that are used as standard initial tests of theory frameworks at the proton drip line have not been considered in the UCOM case (e.g., binding energies, one-proton separation energies, two-proton separation energies).