Reaction mechanisms in transport theories: a test of the nuclear effective interaction

TL;DR

This paper reviews recent theoretical results on collective excitations and reactions in neutron-rich and charge asymmetric nuclear systems, focusing on the role of symmetry energy and isospin effects at Fermi energies.

Contribution

It introduces a detailed analysis of dipole vibrations and the Pygmy Dipole Resonance, highlighting their dependence on symmetry energy and isospin dynamics in nuclear reactions.

Findings

Identification of a low-energy Pygmy Dipole Resonance mode

Sensitivity of resonance strength to symmetry energy below saturation

Insights into isospin effects on dissipation mechanisms in nuclear reactions

Abstract

We review recent results concerning collective excitations in neutron-rich systems and reactions between charge asymmetric systems at Fermi energies. Solving numerically self-consistent transport equations for neutrons and protons with specific initial conditions, we explore the structure of the different dipole vibrations in the $^{132}Sn$ system and investigate their dependence on the symmetry energy. We evidence the existence of a distinctive collective mode, that can be associated with the Pygmy Dipole Resonance, with an energy well below the standard Giant Dipole Resonance and isoscalar-like character, i.e. very weakly dependent on the isovector part of the nuclear effective interaction. At variance, the corresponding strength is rather sensitive to the behavior of the symmetry energy below saturation, which rules the number of excess neutrons in the nuclear surface. In reactions between charge asymmetric systems at Fermi energies, we investigate the interplay between dissipation mechanisms and isospin effects. Observables sensitive to the isospin dependent part of nuclear interaction are discussed, providing information on the symmetry energy density dependence below saturation.