Energy and pressure in neutron matter: current status of ab initio predictions vs. empirical constraints

Modern theoretical predictions of the neutron matter equation of state and the symmetry energy are timely. Recent and planned experiments aim at extracting constraints on the density dependence of these quantities, which is of paramount importance for a number of nuclear and astrophysical systems. We discuss ab initio predictions in relation to recent empirical information. We emphasize and demonstrate that free-space NN data pose stringent constraints on the density dependence of the neutron matter equation of state and thus the slope of the symmetry energy at saturation, which we find to be extremely sensitive to the isovector component of the NN interaction through the ¹S₀ partial wave.