Spontaneous Scalarization and Boson Stars

TL;DR

This paper investigates the conditions under which spontaneous scalarization occurs in Scalar-Tensor boson stars, highlighting the role of boson self-interaction and deriving analytical tools to assess star sensitivity and evolution.

Contribution

It demonstrates that strong boson self-interaction enables scalarization and provides analytical expressions for star sensitivity in Scalar-Tensor theories.

Findings

Scalarization does not occur without boson self-interaction.

Large self-interaction induces scalarization by increasing star compactness.

Derived a formula to compute star sensitivity from mass and particle number.

Abstract

We study spontaneous scalarization in Scalar-Tensor boson stars. We find that scalarization does not occur in stars whose bosons have no self-interaction. We introduce a quartic self-interaction term into the boson Lagrangian and show that when this term is large, scalarization does occur. Strong self-interaction leads to a large value of the compactness (or sensitivity) of the boson star, a necessary condition for scalarization to occur, and we derive an analytical expression for computing the sensitivity of a boson star in Brans-Dicke theory from its mass and particle number. Next we comment on how one can use the sensitivity of a star in any Scalar-Tensor theory to determine how its mass changes when it undergoes gravitational evolution. Finally, in the Appendix, we derive the most general form of the boson wavefunction that minimises the energy of the star when the bosons carry a U(1) charge.