35 research outputs found
Scalar-tensor black holes coupled to Born-Infeld nonlinear electrodynamics
The non-existence of asymptotically flat, neutral black holes and
asymptotically flat, charged black holes in the Maxwell electrodynamics, with
non-trivial scalar field has been proved for a large class of scalar-tensor
theories. The no-scalar-hair theorems, however, do not apply in the case of
non-linear electrodynamics. In the present work numerical solutions describing
charged black holes coupled to Born-Infeld type non-linear electrodynamics in
scalar-tensor theories of gravity with massless scalar field are found. The
causal structure and properties of the solutions are studied, and a comparison
between these solutions and the corresponding solutions in the General
Relativity is made. The presence of the scalar field leads to a much more
simple causal structure. The present class of black holes has a single,
non-degenerate horizon, i.e., its causal structure resembles that of the
Schwarzschild black hole.Comment: 12 pages, 4 figures, PR
Boson stars in massive dilatonic gravity
We study equilibrium configurations of boson stars in the framework of a
class scalar-tensor theories of gravity with massive gravitational scalar
(dilaton). In particular we investigate the influence of the mass of the
dilaton on the boson star structure. We find that the masses of the boson stars
in presence of dilaton are close to those in general relativity and they are
sensitive to the ratio of the boson mass to the dilaton mass within a typical
few percent. It turns out also that the boson star structure is mainly
sensitive to the mass term of the dilaton potential rather to the exact form of
the potential.Comment: 9 pages, latex, 9 figures, one figure dropped, new comments added,
new references added, typos correcte
Structures and waves in a nonlinear heat-conducting medium
The paper is an overview of the main contributions of a Bulgarian team of
researchers to the problem of finding the possible structures and waves in the
open nonlinear heat conducting medium, described by a reaction-diffusion
equation. Being posed and actively worked out by the Russian school of A. A.
Samarskii and S.P. Kurdyumov since the seventies of the last century, this
problem still contains open and challenging questions.Comment: 23 pages, 13 figures, the final publication will appear in Springer
Proceedings in Mathematics and Statistics, Numerical Methods for PDEs:
Theory, Algorithms and their Application