Nuclear Matter and Nuclear Dynamics

1. Introduction The Equation of State (EOS) of nuclear matter plays a fundamental role in the understanding of many aspects of nuclear physics and astrophysics. Transient states of nuclear matter far from normal conditions can be created in terrestrial laboratories and many experimental and theoretical efforts have been devoted to the study of nuclear reactions, from low to intermediate energies, as a possible tool to learn about the behavior of nuclear matter and its EOS. In particular, the availability of exotic beams has opened the way to explore, in laboratory conditions, new aspects of nuclear structure and dynamics up to extreme ratios of neutron (N) to proton (Z) numbers. Over the past years, measurements of isoscalar collective vibrations, collective flows and meson production have contributed to constrain the EOS for symmetric matter for densities up to five time the saturation value [1]. However, the EOS of asymmetric matter has comparatively few experimental constraints: The isovector part of the nuclear effective interaction (Iso-EOS) and the corresponding symmetry energy are largely unknown far from normal density. The knowledge of the EOS of asymmetric matter is very important at low densities, for studies concerning neutron skins, pigmy resonances, nuclear structure at the drip lines, neutron star formation and crust, as well as at high densities, for investigations of neutron star mass-radius relation, cooling, hybrid structure, transition to a deconfined phase, formation of black holes. Hence a large variety of phenomena, involving an enormous range of scales in size, characteristic time and energy, but all based on nuclear processes at fundamental level, are linked by the concept of EOS. From one side, this has stimulated new thorough studies of the ground state energy of (asymmetric) nuclear systems, based on microscopic many-body approaches, from which EOS and effective interactions can be extracted, that are essential for modeling heavy ion collisions (HIC) and the structure of neutron stars [2, 3, 4, 5]. Predictions of different many-body techniques will be compared in Section 2. On the other side, several observables which are sensitive to the Iso-EOS and testable experimentally, have been suggested [6, 7, 8, 9]. Taking advantage of new opportunities in theory (development of rather reliable microscopic transport codes for HIC) and in experiments (availability of very asymmetric radioactive beams, improved possibility of measuring event-by-event correlations), in the following Sections 3-5 we will review new studies aiming to constrain the existing effective interaction models. We will …