Symmetry energy from the nuclear collective motion: constraints from dipole, quadrupole, monopole and spin-dipole resonances

TL;DR

This paper reviews how nuclear collective vibrations, especially giant resonances, provide constraints on the nuclear symmetry energy, crucial for understanding nuclear matter properties near saturation density.

Contribution

It surveys recent experimental and theoretical constraints on the symmetry energy derived from various nuclear collective modes, including dipole, quadrupole, monopole, and spin-dipole resonances.

Findings

Values of symmetry energy around saturation density are deduced from isovector modes.

Isoscalar monopole energy dependence on isotopic variation links to symmetry energy.

Charge-exchange spin-dipole excitations offer indirect access to neutron skin and symmetry energy.

Abstract

The experimental and theoretical studies of Giant Resonances, or more generally of the nuclear collective vibrations, are a well established domain in which sophisticated techniques have been introduced and firm conclusions reached after an effort of several decades. From it, information on the nuclear equation of state can be extracted, albeit not far from usual nuclear densities. In this contribution, which complements other contributions appearing in the current volume, we survey some of the constraints that have been extracted recently concerning the parameters of the nuclear symmetry energy. Isovector modes, in which neutrons and protons are in opposite phase, are a natural source of information and we illustrate the values of symmetry energy around saturation deduced from isovector dipole and isovector quadrupole states. The isotopic dependence of the isoscalar monopole energy has also been suggested to provide a connection to the symmetry energy: relevant theoretical arguments and experimental results are thoroughly discussed. Finally, we consider the case of the charge-exchange spin-dipole excitations in which the sum rule associated with the total strength gives in principle access to the neutron skin and thus, indirectly, to the symmetry energy.