We carry out non-perturbative calculations of the single-particle excitation spectrum in strongly interacting neutron matter. These are microscopic quantum Monte Carlo computations of manyneutron energies at different densities as well as several distinct excited states. As input, we employ both phenomenological and chiral two-and three-nucleon interactions. We use the single-particle spectrum to extract the effective mass in neutron matter. With a view to systematizing the error involved in this extraction, we carefully assess the impact of finite-size effects on the quasiparticle dispersion relation. We find an effective-mass ratio that drops from 1 as the density is increased. We conclude by connecting our results with the physics of ultracold gases as well as with energy-density functional theories of nuclei and neutron-star matter.

We generalize the problem of strongly interacting neutron matter by adding a periodic external modulation. This allows us to study from first principles a neutron system that is extended and inhomogeneous, with connections to the physics of both neutron-star crusts and neutron-rich nuclei. We carry out fully nonperturbative microscopic quantum Monte Carlo calculations of the energy of neutron matter at different densities, as well as different strengths and periodicities of the external potential. In order to remove systematic errors, we examine finite-size effects and the impact of the wave function ansatz. We also make contact with energy-density functional theories of nuclei and disentangle isovector gradient contributions from bulk properties. Finally, we calculate the static density-density linear response function of neutron matter and compare it with the response of other physical systems.

We investigate the problem of periodically modulated strongly interacting neutron matter. We carry out ab initio non-perturbative auxiliary-field diffusion Monte Carlo calculations using an external sinusoidal potential in addition to phenomenological two-and three-nucleon interactions. Several choices for the wave function ansatz are explored and special care is taken to extrapolate finite-sized results to the thermodynamic limit. We perform calculations at various densities as well as at different strengths and periodicities of the one-body potential. Our microscopic results are then used to constrain the isovector term from energy-density functional theories of nuclei at many different densities, while making sure to separate isovector contributions from bulk properties. Lastly, we use our results to extract the static density-density linear response function of neutron matter at different densities. Our findings provide insights into inhomogeneous neutron matter and are related to the physics of neutron-star crusts and neutron-rich nuclei.

Neutron matter is interesting both as an extension of terrestrial nuclear physics and due to its significance for the study of neutron stars. In this work, after some introductory comments on nuclear forces, nuclear ab initio theory, and nuclear phenomenology, we employ two techniques, Quantum Monte Carlo (QMC) and Energy Density Functionals, to practically handle an extended system composed of strongly interacting neutrons. We start by summarizing work on the static response of neutron matter, which considers the impact of external influences on the timeindependent system. We then proceed to discuss new results of the energy of quasiparticle excitations in neutron matter, including QMC calculations with chiral or phenomenological nucleon-nucleon interactions. As part of this study, we carefully study the approach of our finite-number computations toward the infinite-system limit.

Abstract. Complexities greatly limit any study of strongly correlated systems to a small number of particles. Thus, any attempt at understanding infinite systems such as those arising from neutron matter (NM) must consider finite-size (FS) effects at play when below the thermodynamic limit (TL). In these conference proceedings we provide some examples of FS effects at work and discuss our prescription for extrapolating the physics of extended systems. We present our methodology and calculations performed for an assortment of strongly correlated (SC) systems. Ab initio, non-perturbative Quantum Monte Carlo (QMC) methods can be employed to accurately compute ground-state energies and finite-temperature properties. We apply these to periodically modulated NM and use our results to constrain phenomenological theories of nuclei and study the static response of NM.