Generation of scalar-tensor gravity effects in equilibrium state boson stars

TL;DR

This paper models boson stars within Scalar-Tensor Gravity, analyzing their stability and maximum mass, and finds that current constraints make their solutions nearly identical to those in General Relativity, with differences in earlier cosmological eras.

Contribution

It introduces numerical models of boson stars in Scalar-Tensor Gravity considering various couplings and analyzes their stability and mass limits across cosmological eras.

Findings

Current observational constraints make Scalar-Tensor solutions nearly identical to General Relativity.

Maximum stable mass in Scalar-Tensor gravity matches that of General Relativity in the present era.

In earlier eras, the maximum stable mass is smaller and only positive binding energy states are possible.

Abstract

Boson stars in zero-, one-, and two-node equilibrium states are modeled numerically within the framework of Scalar-Tensor Gravity. The complex scalar field is taken to be both massive and self-interacting. Configurations are formed in the case of a linear gravitational scalar coupling (the Brans-Dicke case) and a quadratic coupling which has been used previously in a cosmological context. The coupling parameters and asymptotic value for the gravitational scalar field are chosen so that the known observational constraints on Scalar-Tensor Gravity are satisfied. It is found that the constraints are so restrictive that the field equations of General Relativity and Scalar-Tensor gravity yield virtually identical solutions. We then use catastrophe theory to determine the dynamically stable configurations. It is found that the maximum mass allowed for a stable state in Scalar-Tensor gravity in the present cosmological era is essentially unchanged from that of General Relativity. We also construct boson star configurations appropriate to earlier cosmological eras and find that the maximum mass for stable states is smaller than that predicted by General Relativity, and the more so for earlier eras. However, our results also show that if the cosmological era is early enough then only states with positive binding energy can be constructed.