Finite particle number description of neutron matter using the unitary correlation operator and high-momentum pair methods

TL;DR

This paper develops a finite particle number approach using the unitary correlation operator and high-momentum pair methods to calculate neutron matter equations of state with various nucleon-nucleon interactions, showing good agreement with other microscopic theories.

Contribution

It introduces a combined UCOM and high-momentum pair framework for neutron matter, incorporating short-range, tensor, and spin-orbit correlations with finite particle numbers.

Findings

Converged total energy per particle with increasing 2p2h configurations.

Effects of short-range, tensor, and spin-orbit correlations on energy density.

Agreement with other microscopic many-body calculations, especially AFDMC.

Abstract

By using bare Argonne V4' (AV4'), V6' (AV6'), and V8' (AV8') nucleon-nucleon (NN) interactions respectively, the nuclear equations of state (EOSs) for neutron matter are calculated with the unitary correlation operator and high-momentum pair methods. The neutron matter is described under a finite particle number approach with magic number $N=66$ under a periodic boundary condition. The central short-range correlation coming from the short-range repulsion in the NN interaction is treated by the unitary correlation operator method (UCOM) and the tensor correlation and spin-orbit effects are described by the two-particle two-hole (2p2h) excitations of nucleon pairs, in which the two nucleons with a large relative momentum are regarded as a high-momentum pair (HM). With the 2p2h configurations increasing, the total energy per particle of neutron matter is well converged under this UCOM+HM framework. By comparing the results calculated with AV4', AV6', and AV8' NN interactions, the effects of the short-range correlation, the tensor correlation, and the spin-orbit coupling on the density dependence of the total energy per particle of neutron matter are demonstrated. Moreover, the contribution of each Hamiltonian component to the total energy per particle is discussed. The EOSs of neutron matter calculated within the present UCOM+HM framework agree with the calculations of six different microscopic many-body theories, especially in agreement with the auxiliary field diffusion Monte Carlo calculations.