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Because of the presence of a liquid-gas phase transition in nuclear matter, compactstar matter can present a region of instability against the formation of clusters. We investigate this phase separation in a matter composed of neutrons, protons and electrons, within a Skyrme-Lyon mean-field approach. Matter instability and phase properties are characterized through the study of the free-energy curvature. The effect of β-equilibrium is also analyzed in detail, and we show that the opacity to neutrinos has an influence on the presence of clusterized matter in finite-temperature proto-neutron stars.

We present various properties of nuclear and compact-star matter, comparing the predictions from two kinds of phenomenological approaches: relativistic models (with both constant and density-dependent couplings) and nonrelativistic Skyrme-type interactions. We mainly focus on the liquid-gas instabilities that occur at subsaturation densities, leading to the decomposition of the homogeneous matter into a clusterized phase. Such study is related to the description of neutron-star crust (at zero temperature) and supernova dynamics (at finite temperature).

Asymmetric nuclear matter at sub-saturation densities is shown to present only one type of instabilities. The associated order parameter is dominated by the isoscalar density and so the transition is of liquid-gas type. The instability goes in the direction of a restoration of the isospin symmetry leading to a fractionation phenomenon. These conclusions are model independent since they can be related to the general form of the asymmetry energy. They are illustrated using density functional approaches.Comment: 4 pages, 5 figures, to appear in Phys. Rev.

International audienceCharged product multiplicities and Z distributions were measured for single multifragmenting sources produced in collisions between Full-size image (<1 K) and Full-size image (<1 K) at the same available energy per nucleon. Z distributions are found identical for both reactions while fragment multiplicities scale as the charge of the total systems. A complete dynamical simulation, in which multifragmentation originates in the spinodal decomposition of a finite piece of nuclear matter resulting from an incomplete fusion of projectile and target, well accounts for this experimental observation

The nuclear collective response at finite temperature is investigated for the first time in the quantum framework of the small amplitude limit of the extended TDHF approach, including a non-Markovian collision term. It is shown that the collision width satisfies a secular equation. By employing a Skyrme force, the isoscalar monopole, isovector dipole and isoscalar quadrupole excitations in 40 Ca are calculated and important quantum features are pointed out. The collisional damping due to decay into incoherent 2p-2h states is small at low temperatures but increases rapidly at higher temperatures.

This paper focuses on the isospin properties of the asymmetric nuclear-matter liquid-gas phase transition analyzed in a mean-field approach, using Skyrme effective interactions. We compare two different mechanisms of phase separation for low-density matter: equilibrium and spinodal decomposition. The isospin properties of the phases are deduced from the free-energy curvature, which contains information both on the average isospin content and on the system fluctuations. Some implications on experimentally accessible isospin observables are presented.

A novel method is presented for implementation of the extended mean-field theory incorporating two-body collisions. At a given time, stochastic imaginary time propagation of occupied states are used to generate a convenient basis. The quantal collision terms, including memory effects, is then computed by a backward mean-field propagation of these single-particle states. The method is illustrated in an exactly solvable model. Whereas the usual TDHF fails to reproduce the long time evolution, a good agreement is found between the extended TDHF and the exact solution.