Correlations in nuclear matter at low densities in an extended relativistic mean-field model

Knowledge of the equation of state of strongly interacting matter is required for the description of the variety of nuclear matter phases in a wide range of densities, temperatures, and proton fractions. A specifically important problem is the construction of equations of state for astrophysical applications, e.g for the investigation of various stages of core-collapse supernova explosions and the structure of proto-neutron and neutron stars. For many years, a very small number of equation of state tables was available that have been used in simulations of dynamical astrophysical processes covering the full parameter space needed. These equations of state often do not supply sufficient information on the thermodynamic and compositional details and do not take into account all relevant phase transitions when multiple phases co-exist. In recent years, the appearance of new experimental data on atomic nuclei,heavy-ion-collisions and from astrophysical observations as well as the progress in the theoretical description of the nuclear matter properties and significant improvements of supercomputers have triggered new developments for constructing equations of state. Nevertheless, existing microscopic approaches still do not allow to construct a description in the whole range of densities and temperatures. Thus, approximations and simplifications are needed to develop practical schemes. Thereby, different phenomenological approaches to the equation of state continue to be developed. In this work we study the effect of two specific types of correlations on thermodynamic properties of nuclear matter within the framework of a generalized relativistic mean-field model with light clusters as additional degrees of freedom beyond nucleons. In particular, these correlations include two-body scattering contributions and pairing effects. They appear due to the short-range nucleon-nucleon interaction at low densities and modify the composition and thermodynamic properties of matter. These effects should be included in the ...