Benchmark calculations of infinite neutron matter with realistic two- and three-nucleon potentials

We present the equation of state of infinite neutron matter as obtained from highly realistic Hamiltonians that include nucleon-nucleon and three-nucleon coordinate-space potentials. We benchmark three independent many-body methods: Brueckner-Bethe-Goldstone (BBG), Fermi hypernetted chain/single-operator chain (FHNC/SOC), and auxiliary-field diffusion Monte Carlo (AFDMC). We find them to provide similar equations of state when the Argonne upsilon(18) and the Argonne upsilon(6)' nucleon-nucleon potentials are used in combination with the Urbana IX three-body force. Only at densities larger than about 1.5 the nuclear saturation density (rho(0) = 0.16 fm(-3)) the FHNC/SOC energies are appreciably lower than the other two approaches. The AFDMC calculations carried out with all of the Norfolk potentials fitted to reproduce the experimental trinucleon ground-state energies and nd doublet scattering length yield unphysically bound neutron matter, associated with the formation of neutron droplets. Including tritium beta decay in the fitting procedure, as in the second family of Norfolk potentials, mitigates but does not completely resolve this problem. An excellent agreement between the BBG and AFDMC results is found for the subset of Norfolk interactions that do not make neutron-matter collapse, while the FHNC/SOC equations of state are moderately softer.

Automated summary

In this study, we obtained the equation of state of infinite neutron matter using highly realistic Hamiltonians and benchmarked three independent many-body methods. The results show that these methods provide similar equations of state when specific nucleon-nucleon potentials and three-body forces are used. However, at high densities, one method shows significantly lower energy compared to the others. The study also highlights the possibility of unphysical results when certain parameters are used in the calculations.