Boson stars in Palatini gravity

Abstract

We explore equilibrium solutions of spherically symmetric boson stars in the Palatini formulation of gravity. We account for the modifications introduced in the gravitational sector by using a recently established correspondence between modified gravity with scalar matter and general relativity with modified scalar matter. We focus on the quadratic theory and compare its solutions with those found in general relativity, exploring both positive and negative values of the coupling parameter ξ. As matter source, a complex, massive scalar field with and without self-interaction terms is considered. Our results show that the existence curves of boson stars in Palatini gravity are fairly similar to those found in general relativity. Major differences are observed for negative values of the coupling parameter which results in a repulsive gravitational component for high enough scalar field density distributions. Adding self-interactions makes the degeneracy between and general relativity even more pronounced, leaving very little room for observational discrimination between the two theories.