Charged Ising Model of Neutron Star Matter

TL;DR

This paper introduces the Charged-Ising Model, a lattice-gas simulation approach for neutron-star crust matter, capturing Coulomb frustration effects and enabling efficient large-scale Monte Carlo studies of nuclear pasta structures.

Contribution

A new lattice-gas model (CIM) for neutron-star matter is proposed, efficiently simulating Coulomb frustration effects in the crust with pre-computed long-range interactions.

Findings

CIM reproduces key features of Coulomb frustration in neutron-star crusts.

Pre-computation of Coulomb interactions significantly reduces simulation time.

Results include heat capacity, pair-correlation, and structure factor across conditions.

Abstract

Background: The inner crust of a neutron star is believed to consist of Coulomb-frustrated complex structures known as "nuclear pasta" that display interesting and unique low-energy dynamics. Purpose: To elucidate the structure and composition of the neutron-star crust as a function of temperature, density, and proton fraction. Methods: A new lattice-gas model, the "Charged-Ising Model" (CIM), is introduced to simulate the behavior of neutron-star matter. Preliminary Monte Carlo simulations on 30^3 lattices are performed for a variety of temperatures, densities, and proton fractions. Results: Results are obtained for the heat capacity, pair-correlation function, and static structure factor for a variety of conditions appropriate to the inner stellar crust. Conclusions: Although relatively simple, the CIM captures the essence of Coulomb frustration that is required to simulate the subtle dynamics of the inner stellar crust. Moreover, the computationally demanding long-range Coulomb interactions have been pre-computed at the appropriate lattice sites prior to the start of the simulation resulting in enormous computational gains. This work demonstrates the feasibility of future CIM simulations involving a large number of particles as a function of density, temperature, and proton fraction.