The isoscalar features of Pygmy Dipole Resonance: a subtle game of symmetry energy

TL;DR

This paper explores the isoscalar characteristics of Pygmy Dipole Resonance (PDR) by analyzing how nuclear symmetry energy influences its structure, revealing a complex interplay between neutron skin dynamics and core polarization.

Contribution

It introduces a new perspective on PDR, linking its features to the density dependence of symmetry energy and combined neutron skin-core dynamics within a quantum many-body framework.

Findings

The symmetry energy variation shapes the low-lying dipole response.

PDR features result from neutron skin and core polarization interplay.

Insights into the transition from skin oscillation to bulk dynamics.

Abstract

The vibrational structure of the Pygmy Dipole Resonance (PDR) is investigated within a quantum many-body treatment with extended separable interactions able to encode the dependence of nuclear symmetry energy on density. A new picture of PDR is unveiled in terms of a combined dynamics of the neutron skin and of the core isovector polarization, which determines the isoscalar features of PDR while reproducing the isovector properties of Giant Dipole Resonance. The key role played by the variation with density of the symmetry energy on shaping the low-lying dipole response and its isoscalar-isovector structure is underlined. Our results provide insights for the challenge of clarifying the transition from skin oscillation to a highly bulk collective dynamics.