Bayesian inference on nuclear data and neutron star observations for the nuclear equation of state

Pietro Klausner (Università degli Studi di Milano, Italy & LPC Caen, France)

Our objective is to study the nuclear Equation of State (EoS) using experimental observations from both nuclear physics and astrophysics. Within the standard Skyrme functional ansatz, we build a reliable probability distribution for a combination of nuclear matter parameters (NMP) and Skyrme parameters (which are needed to constrain all the terms of the functional) using a combined Bayesian inference of a large set of EoS-sensitive nuclear structure data. Beyond the usual ground state properties like binding energies and charge radii, we also included the much-discussed polarizabilities and parity-violating asymmetries of 208Pb and 48Ca. The result is a multivariate probability distribution for the NMPs and Skyrme parameters. One of the most delicate aspects of the analysis was handling the uncertainties associated with each measurement, as Skyrme energy density functionals cannot always reproduce experimental data within experimental errors, particularly for binding energies. This led us to discover an interplay between the binding energies and the polarizabilities of 208Pb and 48Ca, which favours a soft nuclear equation of state.
Furthermore, the posterior distribution can be used as a prior distribution in a successive Bayesian analysis, this time using astrophysical observations as constraints. In this way, this second posterior distribution of NMPs will be informed by both nuclear physics and astrophysics. The constraints from nuclear experiments are well compatible with the theoretical predictions for infinite pure neutron matter from ab-initio modelling, and those constraints additionally indicate the existence of interesting structures in the EoS of neutron stars. We will discuss the final predictions on some selected static properties of neutron stars, which can be computed from the distribution of NMPs. Further attention will be given to the composition of the star crust, which is computed consistently with the star EoS within the extended Thomas-Fermi formalism.