Solitonic and Non-Solitonic Q-Stars

The properties of several types of Q-stars are studied and compared with their flat space analogues, i.e. Q-balls. The analysis is based on calculating the mass, global U(1) charge and binding energy for families of solutions parametrized by the central value of the scalar field. The two most frequently used Q-star models (differing by their potential term) are studied. Although there are general similarities between both Q-star types, there are important differences as well as new features with respect to the non-gravitating systems. We find non-solitonic solutions which do not have a flat space limit, in the weak (scalar) field region as well as in the opposite region of strong central scalar field for which there does not exist Q-ball solutions at all.Comment: To appear in the proceedings of 11th Marcel Grossmann Meeting, Berlin, July 200

Spherical Structures in Conformal Gravity and its Scalar-Tensor Extension

We study spherically-symmetric structures in Conformal Gravity and in a scalar-tensor extension and gain some more insight about these gravitational theories. In both cases we analyze solutions in two systems: perfect fluid solutions and boson stars of a self-interacting complex scalar field. In the purely tensorial (original) theory we find in a certain domain of parameter space finite mass solutions with a linear gravitational potential but without a Newtonian contribution. The scalar-tensor theory exhibits a very rich structure of solutions whose main properties are discussed. Among them, solutions with a finite radial extension, open solutions with a linear potential and logarithmic modifications and also a (scalar-tensor) gravitational soliton. This may also be viewed as a static self-gravitating boson star in purely tensorial Conformal Gravity.Comment: 24 pages, revised version, accepted for publication in Phys. Rev.

Spherical Non-Abelian Solutions in Conformal Gravity

We study static spherically-symmetric solutions of non-Abelian gauge theory coupled to Conformal Gravity. We find solutions for the self-gravitating pure Yang-Mills case as well as monopole-like solutions of the Higgs system. The former are localized enough to have finite mass and approach asymptotically the vacuum geometry of Conformal Gravity, while the latter do not decay fast enough to have analogous properties.Comment: 12 pages, revised version, accepted for publication in Phys. Rev.

Cylindrically-Symmetric Solutions in Conformal Gravity

Cylindrically-symmetric solutions in Conformal Gravity are investigated and several new solutions are presented and discussed. Among them, a family of vacuum solutions, generalizations of the Melvin solution and cosmic strings of the Abelian Higgs model. The Melvin-like solutions have finite energy per unit length, while the string-like solutions do not.Comment: 22 pages, revised version, accepted for publication in Phys. Rev.

Magnetic Black Holes in the Vector-Tensor Horndeski Theory

We construct novel exact solutions of magnetically charged Black Holes in the vector-tensor Horndeski gravity and discuss their main features. Unlike the analogous electric case, the field equations are linear in a simple (quite standard) parametrization of the metric tensor and they can be solved analytically. The solutions are presented in terms of hypergeometric functions which makes the analysis of the black hole properties relatively straightforward. Some of the aspects of these black holes are quite ordinary like the existence of extremal configurations with maximal magnetic charge for a given mass, or the existence of a mass with maximal temperature for a given charge, but others are somewhat unexpected, like the existence of black holes with a repulsive gravitational field. We perform our analysis for both signs of the non-minimal coupling constant and find black hole solutions in both cases but with significant differences between them. The most prominent difference is the fact that the black holes for the negative coupling constant have a spherical surface of curvature singularity rather than a single point. On the other hand, the gravitational field produced around this kind of black holes is always attractive. Also, for small enough magnetic charge and negative coupling constant, extremal black holes do not exist and all magnetic black holes have a single horizon.Comment: A few sentences rephrased and some misprints correcte