161 research outputs found
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
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