Nuclear pasta structures and symmetry energy

Abstract

In the framework of the relativistic mean field model with Thomas-Fermi approximation, we study the structures of low density nuclear matter in a three-dimensional geometry with reflection symmetry. The numerical accuracy and efficiency are improved by expanding the mean fields according to fast cosine transformation and considering only one octant of the unit cell. The effect of finite cell size is treated carefully by searching for the optimum cell size. Typical pasta structures (droplet, rod, slab, tube, and bubble) arranged in various crystalline configurations are obtained for both fixed proton fractions and β-equilibration. It is found that the properties of droplets/bubbles are similar in body-centered cubic (BCC) and face-centered cubic (FCC) lattices, where the FCC lattice generally becomes more stable than BCC lattice as density increases. For the rod/tube phases, the honeycomb lattice is always more stable than the simple one. By introducing an ω-ρ cross coupling term, we further examine the pasta structures with a smaller slope of symmetry energy L = 41.34 MeV, which predicts larger onset densities for core-crust transition and nonspherical nuclei. Such a variation due to the reduction of L is expected to have impacts on various properties in neutron stars, supernova dynamics, and binary neutron star mergers.

Tasting Nuclear Pasta Made with Classical Molecular Dynamics Simulations

“…Often, the energy minima are very close to each other. The realization of various shapes are thus somewhat model dependent and the transition from one shape to another depends sensitively on the nuclear physics inputs, such as the nuclear equation of state especially its symmetry energy term [10,[17][18][19][20]. Both static and dynamic approaches using various nuclear interactions and assumptions about the composition of neutron stars have been used in studying the formation, properties and phase transition of nuclear pasta by many groups over the last three decades.…”