# Pygmy resonances and symmetry energy

## TL;DR

This paper reviews three decades of research on pygmy resonances in nuclei, their connection to the symmetry energy of nuclear matter, and implications for neutron star properties.

## Contribution

It summarizes experimental and theoretical progress on pygmy resonances and their relation to the symmetry energy, highlighting correlations with neutron skins and neutron star characteristics.

## Key findings

- Identification of pygmy resonances in medium and heavy nuclei
- Correlation between pygmy resonances and the slope parameter of symmetry energy
- Implications for neutron star properties

## Abstract

I present a brief summary of the first three decades of studies of pygmy resonances in nuclei and their relation to the symmetry energy of nuclear matter. I discuss the first experiments and theories dedicated to study the electromagnetic response in halo nuclei and how a low energy peak was initially identified as a candidate for the pygmy resonance. This is followed by the description of a collective state in medium heavy and heavy nuclei which was definitely identified as a pygmy resonance. The role of the slope parameter of the symmetry energy in determining the properties of neutron stars is stressed. The theoretical and experimental information collected on pygmy resonances, neutron skins, and the numerous correlations found with the slope parameter is briefly reviewed.