Abstract
Interiors of neutron stars are ultra-dense and may contain a core of deconfined quark matter. Such a core connects to the outer layers smoothly or through a sharp microscopic interface or through an intermediate macroscopic layer of inhomogeneous mixed phases, which is globally neutral but locally contains electrically charged domains. Here I employ a nucleon-meson model under neutron star conditions that shows a first-order chiral phase transition at large densities. In the vicinity of this chiral transition I calculate the free energies of various mixed phases - different 'pasta structures' - in the Wigner-Seitz approximation. Crucially, chirally broken nuclear matter and the approximately chirally symmetric phase (loosely interpreted as quark matter) are treated on the same footing. This allows me to compute the interface profiles of bubbles, rods, and slabs fully consistently, taking into account electromagnetic screening effects and without needing the surface tension as an input. I find that the full numerical results tend to disfavor mixed phases compared to a simple step-like approximation used frequently in the literature and that the predominantly favored pasta structure consists of slabs with a surface tension $\Sigma \simeq 6\, {\rm MeV}/{\rm fm}^2$.
Highlights
Neutron stars probe a large range of baryon densities, from subsaturation densities in the outer layers up to several times nuclear saturation density in the core
I have first identified the region in the vicinity of this phase transition where globally, but not locally, neutral mixed phases are possible without taking into account surface and Coulomb effects
These effects have been taken into account by calculating the profiles of the meson condensates and the electrostatic potential in a consistent way, solving the Euler-Lagrange equations for the condensates coupled with the Poisson equation for the electrostatic potential
Summary
Neutron stars probe a large range of baryon densities, from subsaturation densities in the outer layers up to several times nuclear saturation density in the core. Nuclear and quark matter are treated with two different models [21,22,23,24,25,26,27,28,29,30] In this approach, the profile of a quark-hadron interface cannot be calculated microscopically since this requires knowledge of an effective potential that connects the two phases. By requiring that in the vacuum hχi 1⁄4 fπ, the pion mass term fixes a1 1⁄4 m2π with the pion mass mπ ≃ 139 MeV, as well as the explicit chiral symmetry breaking term ε 1⁄4 m2πfπ In addition to these parameters, the model contains the coupling constants gσ, gω, gρ, which determine the nucleon-meson coupling via Yukawa interactions.
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call