Q-balls in K-field theory

TL;DR

This paper investigates the existence and stability of Q-balls within noncanonical scalar field theories, extending stability criteria and analyzing perturbation behavior, revealing that modifications can enhance Q-ball stability by lowering charge and energy.

Contribution

It extends the Vakhitov-Kolokolov stability criterion to K-field theories and derives conditions for well-posed perturbations, providing new insights into Q-ball stability in noncanonical models.

Findings

Perturbations propagate at speeds different from light.

Noncanonical fields can lower Q-ball charge and energy.

Derived conditions for hyperbolicity of perturbations.

Abstract

We study the existence and stability of Q-balls in noncanonical scalar field theories, $K(|\Phi|^2,X)$ where $\Phi$ is the complex scalar field and $X$ is the kinetic term. We extend the Vakhitov-Kolokolov stability criterion to K-field theories. We derive the condition for the perturbations to have a well-posed Cauchy problem. We find that $K_{,X}>0$ and $K_{,X}+XK_{,XX}>0$ are necessary but not sufficient conditions. The perturbations define a strongly hyperbolic system if $(K_{,X}-2\phi'^2 K_{,XX})(K_{,X}+2\omega^2\phi^2 K_{,XX}) > 0$. For all modifications studied, we found that perturbations propagate at a speed different from light. Generically, the noncanonical scalar field can lower the charge and energy of the Q-ball and therefore improves its stability.