Boson Stars surrounded by Polish Doughnuts in Scalar-Tensor Theory

TL;DR

This paper explores how scalarization in boson stars within scalar-tensor theories alters spacetime, leading to unique accretion disk structures that could serve as observational signatures of alternative gravity models.

Contribution

It presents the first detailed analysis of thick accretion disks around scalarized boson stars, revealing significant qualitative differences from general relativity.

Findings

Scalarized boson stars can lack innermost circular orbits, allowing stable motion down to the center.

Disks around scalarized boson stars are more compact and strongly bound.

Non-monotonic angular momentum profiles enable two-centered disk configurations.

Abstract

We investigate thick accretion disks (Polish Doughnuts) around rotating self-interacting boson stars in general relativity and scalar-tensor theories, focusing on spontaneously scalarized solutions and their general relativistic counterparts. Using equilibrium models with constant specific angular momentum, we analyze disk structures across the parameter space, with emphasis on the phase transition between GR and scalarized configurations. We find that scalarization induces qualitative changes in the spacetime that significantly affect disk morphology. In particular, scalarized boson stars can lack innermost circular orbits, allowing stable motion down to the center and enabling highly compact, quasi-spherical disks. For the most massive scalarized solutions, a non-monotonic angular momentum profile further permits two-centered disk configurations connected by a cusp. Overall, disks around scalarized boson stars are more compact and more strongly bound than those in general relativity, highlighting distinctive features that may serve as observational signatures of alternative gravity theories in the strong-field regime.