Applications of chiral forces up to N3LO to finite nuclei and neutron stars

Abstract:   The exciting physics of neutron-rich matter covers a wide range of densities, from finite nuclei to neutron stars. Constraining the neutron-rich matter equation of state (EOS) simultaneously from experiment, observation, and theory is a very active field of research. In anticipation of novel constraints, e.g., from FRIB and multi-messenger astronomy, it is time to take advantage of the recent advances in chiral effective field theory (EFT) and many-body frameworks to improve microscopic predictions of the EOS based on chiral nuclear interactions. I will discuss several applications of a novel Monte Carlo framework for many-body perturbation theory to infinite nuclear matter with chiral two-, three-, and four-nucleon interactions. The efficiency of this framework allows for the incorporation of all many-body contributions up to high orders as well as the Bayesian estimation of theoretical uncertainties through order-by-order calculations. I will show results for the EOS of neutron and symmetric matter, the nuclear saturation point, the symmetry energy as well as its slope parameter, and a comparison to results based on quark-gluon degrees of freedom at intermediate densities. Nuclear matter is furthermore an ideal testbed for the development of chiral interactions aimed at precise nuclear structure and reaction calculations with quantifiable uncertainties across a wide range of the nuclear chart. As a first step, we fit chiral interactions up to next-to-next-to-next-to-leading order (N3LO) to the triton as well as the empirical saturation point. Such approaches have recently gained much attention since ab initio calculations of medium-mass to heavy nuclei have demonstrated that realistic saturation properties of chiral forces in infinite matter are important for reproducing experimental ground-state energies and charge radii. I will review our subsequent study of closed-shell medium-mass nuclei up to nickel using the ab initio In-Medium Similarity Renormalization Group (IM-SRG) and my conclusions for making progress in this direction.