Relativistic effective interaction for nuclei, giant resonances, and neutron stars

Abstract

Nuclear effective interactions are useful tools in astrophysical applications especially if one can guide the extrapolations to the extremes regions of isospin and density that are required to simulate dense, neutron-rich systems. Isospin extrapolations may be constrained in the laboratory by measuring the neutron skin thickness of a heavy nucleus, such as $^{208}\mathrm{Pb}$. Similarly, future observations of massive neutron stars will constrain the extrapolations to the high-density domain. In this contribution we introduce a new relativistic effective interaction that is simultaneously constrained by the properties of finite nuclei, their collective excitations, and neutron-star properties. By adjusting two of the empirical parameters of the theory, one can efficiently tune the neutron skin thickness of $^{208}\mathrm{Pb}$ and the maximum neutron-star mass. We illustrate this procedure in response to the recent interpretation of x-ray observations by Steiner, Lattimer, and Brown that suggests that the FSUGold effective interaction predicts neutron-star radii that are too large and a maximum stellar mass that is too small. The new effective interaction is fitted to a neutron skin thickness in $^{208}\mathrm{Pb}$ of only ${R}_{n}\ensuremath{-}{R}_{p}=0.16$ fm and yields a moderately large maximum neutron-star mass of 1.94 ${M}_{\ensuremath{\bigodot}}$.