Chains of Boson Stars

TL;DR

This paper investigates multi-soliton solutions called chains of boson stars in scalar field theory coupled to gravity, revealing their complex mass-frequency behavior and the effects of gravitational coupling on their structure.

Contribution

It introduces and analyzes axially symmetric multi-soliton solutions, or chains, of boson stars, highlighting their unique mass and charge behaviors depending on the number of constituents and gravitational coupling.

Findings

Chains with odd constituents show spiraling mass-frequency behavior at low coupling.

Higher gravitational coupling causes inner spiral merging with radially excited boson star branches.

Even constituent chains exhibit truncated spirals ending at finite mass and charge.

Abstract

We study axially symmetric multi-soliton solutions of a complex scalar field theory with a sextic potential, minimally coupled to Einstein's gravity. These solutions carry no angular momentum and can be classified by the number of nodes of the scalar field, $k_z$, along the symmetry axis; they are interpreted as chains with $k_z+1$ boson stars, bound by gravity, but kept apart by repulsive scalar interactions. Chains with an odd number of constituents show a spiraling behavior for their ADM mass (and Noether charge) in terms of their angular frequency, similarly to a single fundamental boson star, as long as the gravitational coupling is small; for larger coupling, however, the inner part of the spiral is replaced by a merging with the fundamental branch of radially excited spherical boson stars. Chains with an even number of constituents exhibit a truncated spiral pattern, with only two or three branches, ending at a limiting solution with finite values of ADM mass and Noether charge.