Cluster correlations in dilute matter and equation of state

Abstract

Cluster correlations are an important feature in strongly interacting matter at subsaturation densities. They modify the chemical composition of the system and the thermodynamic properties, which are encoded in the equation of state. The formation and dissolution of clusters can be described in a generalized relativistic density functional approach. Clusters are included as explicit degrees of freedom with medium-dependent properties. They are considered as quasiparticles with scalar and vector self-energies that represent the effective in-medium interaction. Essential ingredients in the self-energies are rearrangement contributions, which guarantee the thermodynamic consistency of the model, and mass shifts of composite particles, which take into account the effects of the Pauli exclusion principle. They cause the dissolution of clusters at high densities. The occurence of α-particle clusters on the surface of heavy nuclei can be considered by adapting the generalized relativistic density functional approach to nuclear structure calculations. A systematic variation of the α-particle abundance and neutron skin thickness with the neutron excess of the nucleus and the strength of the isovector contribution to the effective interaction is observed. The surface a clustering affects the correlation of the neutron skin thickness of heavy nuclei with the density dependence of the symmetry energy, which is relevant for calculations of neutron star structure.