Gravitational confinement of ghost scalar fields in neutron stars

TL;DR

This paper explores how ghost scalar fields with negative kinetic energy can be gravitationally confined within neutron stars, revealing stable configurations and oscillatory behaviors through analytical and numerical methods.

Contribution

It demonstrates the existence of stable, non-fine-tuned neutron star configurations containing ghost matter and analyzes their dynamic oscillations.

Findings

Neutron stars can confine ghost scalar fields gravitationally.

Configurations support continuous families of equilibrium solutions.

Neutron stars exhibit persistent oscillations synchronized with ghost scalar modes.

Abstract

We investigate the effects, stability, and nonlinear dynamics of ghost scalar matter modeled as a field with a negative kinetic term confined within the cores of neutron stars. To this end, we analyze static configurations of the coupled Einstein-Euler-(ghost, complex) Klein-Gordon system and then we perform fully dynamical numerical evolutions of illustrative cases. Our results demonstrate that neutron stars can gravitationally confine a finite amount of ghost matter and support continuous families of equilibrium solutions, indicating that these configurations are not the result of fine tuning. We analyze the properties of the final states and find that the neutron star undergoes a persistent pulse-like oscillatory motion. In particular, we explicitly compute the frequency synchronization between the stellar fluid oscillation modes and those of the ghost scalar sector.