Relativistic Lagrangians for finite nuclei and dense matter – RELANSE

This ANR project RELANSE explores matter properties in a regime where the theory of the strong interaction, the quantum chromo-dynamics (QCD), could not be applied directly because of its non-perturbative nature at low-energy. This theory predicts however the onset of a chiral field emerging spontaneously at low-energy as well as the color confinement. These two properties imply that nucleons and mesons are the important degrees of freedom at low-energy. In this project, we develop an innovative, effective and relativistic approach describing chiral, nucleon and meson fields, and we contribute to consolidate the unified description of finite nuclei and neutron stars. The uniqueness of our project lies in the fact that we consistently analyze model predictions based on Hartree and Hartree-Fock approaches, which are adjusted to the same data. In particular, we address the question of the relativistic description of dense matter, where the sound speed, for instance, becomes comparable to the speed of light.
The originality of our project is to anchor the relativistic approaches employed in finite nuclei to the phenomenology of the quark substructure, e.g. results from Lattice QCD, the nucleon polarizability, VDM and quark model. In this way, the in-medium effects appear in our model in a very simple and traceable way compared to currently employed ones and our approach provides a robust guide to predict the properties of dense matter existing in neutron stars. We employ Bayesian statistics to compare the different scenarios to nuclear and astrophysical data, e.g., gravitational waves, x-ray emission from neutron stars. In this framework the theoretical, experimental and astrophysical uncertainties are employed in order to estimate the goodness of our new models.
For finite nuclei, we investigate the impact of the new models on ground state properties, e.g. energies, radii, neutron skin, as well as deformation, clustering, alpha decay and their experimental consequences. The novelty of our model is to possibly reduce the computing time of the present approaches, which employ density-dependent coupling constants. We estimate that our models can be as accurate as the present ones, and our project is instrumental to demonstrate it. We use all existing data to further constraint our models, we investigate the question of the understanding of the parity violating electron scattering puzzle from PREX and CREX experiments, and we address the description of exotic nuclei.
For neutron stars, we complement our relativistic models considering different scenarios for dense matter. Our methodology consists in exploring all various equations of state, which explore the current theoretical uncertainties in the existence of new phases of matter at high density, e.g. quark matter, hyperonic matter, quarkyonic matter. We then compare the predictions of these various scenarios to astrophysical data and we investigate to what extent these data indicate a preference for one of the scenarios describing the core of neutron stars.
The development of new effective Lagrangians helps us to address fundamental questions related to the strong force in dense matter and the Bayesian approach establishes the link between these fundamental properties and the existing data in finite nuclei and in neutron stars. We want to understand how the gaps between first principle, finite nuclei and neutron stars could be bridged and which effective properties of QCD are crucial in dense matter and low-energy. In addition, we will explore dense and finite temperature phases and produce new tables suitable for astrophysical simulations of core-collapse supenovae and kilonovae from neutron star mergers.
In addition, all data and codes from our project will be made publicly available (open-access) and a user-friendly interface in python will be provided to the community.