Charged boson stars and black holes with nonminimal coupling to gravity

Abstract

We find new spherically symmetric charged boson star solutions of a complex scalar field coupled nonminimally to gravity by a "John-type" term of Horndeski theory, that is a coupling between the kinetic scalar term and Einstein tensor. We study the parameter space of the solutions and find two distinct families according to their position in parameter space. More widespread is the family of solutions (which we call branch 1) existing for a finite interval of the central value of the scalar field starting from zero and ending at some finite maximal value. This branch contains as a special case the charged boson stars of the minimally coupled theory. In some regions of parameter space we find a new second branch ("branch 2") of solutions which are more massive and more stable than those of branch 1. This second branch exists also in a finite interval of the central value of the scalar field, but its end points (either both or in some cases only one) are extremal Reissner-Nordström black hole solutions.

Boson stars in Palatini $f(\mathcal{R})$ gravity

“…Given that f (R) theories [32][33][34] offer a large amount of freedom while keeping the field equations within reasonable limits of simplicity, in this work we will explore the impact that high-energy modifications of the gravitational interaction of the f (R) type could have on the astrophysical properties of boson stars. Similar studies have already been carried out in other theories of gravity, such as in scalar-tensor theories [35], Horndeski theories [36,37], and theories with Gauss-Bonnet couplings [38][39][40], among others.…”

Scalarized compact objects in a vector-tensor Horndeski gravity

“…Furthermore, the invariants R, K are finite everywhere including the horizon r h in spite of the fact that the value a(r h ) becomes very small. We noticed a similar phenomenon for charged boson stars in a scalar-tensor Horndeski theory of the "John type" [26] where in certain circumstances a boson star loses its scalar hair and turns into an extremal RN black hole.…”

Slowly rotating black hole solution in the scalar-tensor theory with nonminimal derivative coupling and its thermodynamics

“…It was shown [47,48] that the most substantial approach to the definition of entropy is based on the method proposed by Wald [61,62] which relies upon the Noether conserved quantities. In our case we also used Wald procedure and obtained the expressions for the black hole's mass (56), entropy (59) and the first law (64). The entropy we obtained is proportional to the area of horizon A but has some factor which appears due to nonminimal coupling and the obtained relation is in full agreement with corresponding formulas in [47,48].…”

“…Stable black hole solution in shiftsymmetric Horndeski theory was examined in [52]. Neutron and boson stars in the theory with nonminimal derivative coupling were investigated [53,54,55,56]. Black holes with nonminimal coupling and Gauss-Bonnet term were examined [57,58].…”