Gyroid Phase in Nuclear Pasta

TL;DR

This paper explores the potential existence of gyroid and double-diamond structures in nuclear pasta, using a liquid drop model to evaluate their energies, suggesting these complex morphologies may occur in neutron star crusts.

Contribution

It introduces the possibility of gyroid and double-diamond phases in nuclear pasta, expanding the known structural diversity in subnuclear nuclear matter.

Findings

Gyroid structures may form near the transition from cylinders to slabs.

The volume fraction at the phase transition is similar to that in polymer systems.

More detailed studies on nuclear pasta structures are needed.

Abstract

Nuclear matter is considered to be inhomogeneous at subnuclear densities that are realized in supernova cores and neutron star crusts, and the structures of nuclear matter change from spheres to cylinders, slabs, cylindrical holes and spherical holes as the density increases. In this letter, we discuss other possible structures, that is, gyroid and double-diamond morphologies, which are periodic bicontinuous structures discovered in a block copolymer. Utilizing the compressible liquid drop model, we evaluate their surface and Coulomb energies and show that there is a chance of gyroid appearance near the transition point from a cylinder to a slab. This interesting analogy between nuclear and polymer systems is not merely qualitative. The volume fraction at the phase transition is also similar for the two systems. Although the five shapes listed initially have been long thought to be the only major constituents of so-called nuclear pasta at subnuclear densities, our findings imply that this may not be the case and suggest that more detailed studies on nuclear pasta including the gyroid phase are needed.