42 research outputs found
On Stationary Axially Symmetric Solutions in Brans-Dicke Theory
Stationary, axially symmetric Brans-Dicke-Maxwell solutions are reexamined in
the framework of the Brans-Dicke (BD) theory. We see that, employing a
particular parametrization of the standard axially symmetric metric simplifies
the procedure of obtaining the Ernst equations for axially symmetric
electrovacuum space-times for this theory. This analysis also permits us to
construct a two parameter extension in both Jordan and Einstein frames of an
old solution generating technique frequently used to construct axially
symmetric solutions for BD theory from a seed solution of general relativity.
As applications of this technique, several known and new solutions are
constructed including a general axially symmetric BD-Maxwell solution of
Plebanski-Demianski with vanishing cosmological constant, i.e. the Kinnersley
solution and general magnetized Kerr-Newman--type solutions. Some physical
properties and the circular motion of test particles for a particular subclass
of Kinnersley solution, i.e., a Kerr-Newman-NUT--type solution for BD theory,
are also investigated in some detail.Comment: V2: 18 pages, published version; some references and section VI is
added. V1:17 pages, Revte
Multi-Scalar-Tensor Equivalents for Modified Gravitational Actions
A general scheme of constructing scalar-tensor equivalents to modified
gravitational actions are studied using the algebra of exterior differential
forms and the first order formalism that allows an independent connection and
coframe. By introducing appropriate constraints on the connection,
pseudo-Riemannian cases as well as non-Riemannian cases are discussed for
various gravitational models. The issue of the dynamical degree of freedom for
the resulting scalar fields is discussed at the level of the field equations.
Explicit scalar-tensor equivalents for gravitational models based on
models, the quadratic curvature lagrangians and the models involving the
gradients of the scalar curvature are presented. In particular, explicit ST
equivalence for gravitational lagrangians popular in some cosmological models
are constructed.Comment: V1:17 pages in two column format, revtex; V2: 19 pages, an appendix
and references added, published versio
Linearized modified gravity theories with a cosmological term: advance of perihelion and deflection of light
Two different ways of generalizing Einstein's general theory of relativity
with a cosmological constant to Brans-Dicke type scalar-tensor theories are
investigated in the linearized field approximation. In the first case a
cosmological constant term is coupled to a scalar field linearly whereas in the
second case an arbitrary potential plays the role of a variable cosmological
term. We see that the former configuration leads to a massless scalar field
whereas the latter leads to a massive scalar field. General solutions of these
linearized field equations for both cases are obtained corresponding to a
static point mass. Geodesics of these solutions are also presented and solar
system effects such as the advance of the perihelion, deflection of light rays
and gravitational redshift were discussed. In general relativity cosmological
constant has no role on these phenomena. We see that for the Brans-Dicke theory
the cosmological constant has also no effect on these phenomena. This is
because solar system observations require very large values of the Brans-Dicke
parameter and the correction terms to these phenomena becomes identical to GR
for these large values of this parameter. This result is also observed for the
theory with arbitrary potential if the mass of the scalar field is very light.
For a very heavy scalar field, however, there is no such limit on the value of
this parameter and there are ranges of this parameter where these contributions
may become relevant in these scales. Galactic and intergalactic dynamics is
also discussed for these theories at the latter part of the paper with similar
conclusions.Comment: 25 pages, Revtex. V2: two new sections discussing galactic and
intergalactic phenomena are added, discussion is extended, references added,
Published version
Brans-Dicke-Maxwell Solutions for Higher Dimensional Static Cylindrical Symmetric Spacetime
In this paper, Brans-Dicke-Maxwell type vacuum solutions are considered for a
static cylindrically symmetric spacetime in arbitrary dimensions. Exact
solutions are obtained by directly solving the field equations for the case
where an azimuthal magnetic field is present. Other configurations such as
axial magnetic field case can be obtained by suitably relabeling the
coordinates. We have also considered conformally related "Einstein frame" to
relate the solutions we have obtained with the dilaton-Maxwell type solutions
that exist in the literature. We see that for a special case the general
solution we present reduces to Dilaton-Melvin spacetime. The General
Relativistic limit of these solutions are also discussed and we found that this
limit is different from the four dimensional case.Comment: 9 Pages, articl
Gravitational waves in Brans-Dicke Theory with a cosmological constant
Weak field gravitational wave solutions are investigated in Brans-Dicke (BD)
theory in the presence of a cosmological constant. In this setting the
background geometry is not flat but asymptotically de-Sitter. We investigate
the linearised field equations, and their gravitational wave solutions in a
certain gauge choice. We will show that this theory leads to massless scalar
waves as in original BD theory and in contrast to massive BD theory. The
effects of these waves on free particles and their polarization properties are
studied extensively and effects of the cosmological constant is analyzed in
these phenomena in detail. The energy flux of these waves are also discussed in
this background. By analyzing this flux, we obtain a critical distance where
the waves cannot propagate further, which extends Cosmic no Hair Conjecture
(CNC) to BD theory with a cosmological constant.Comment: 27 pages, Revtex 4-
Superradiance of a Global Monopole in Reissner-Nordstr\"{o}m(-AdS) Space-time
In this article, the behaviour of a charged and massive scalar field around a
global monopole swallowed by a Reissner-Nordstr\"{o}m-Anti-de Sitter (RN-AdS)
black hole is investigated by considering the Klein-Gordon equation in this
geometry. The superradiance phenomenon and instability behaviour of the black
hole against charged scalar perturbations are studied for both an RN-AdS case
and also for an RN black hole surrounded by a reflective mirror, i.e., the
black hole bomb case. The effects of the monopole on these cases are discussed
analytically and also with the help of several graphs in detail. The monopole
charge affects the superradiance threshold frequency and also effects the
instability time scale for both cases. The existence of global monopole makes
these black holes more stable against superradiance instability.Comment: V3: 19 pages, 3 figures, references added, introduction is extended,
Revtex, Published versio
Bending of Light from Reissner-Nordstr\"om-de Sitter-Monopole Black Hole
We study light deflection from a Reissner-Nordstr\"om-de Sitter black hole in
the gravitational monopole background. We first calculate the orbit equation
and the contribution of the monopole and black hole parameters to the
deflection angle up to second-order for the vanishing cosmological constant
case using the Rindler-Ishak method. We also obtain the contribution of the
cosmological constant to light deflection in this geometry in the weak field
limit using the same method.Comment: v2: 10 pages, 2 figures, matches the published versio
Cylindrically Symmetric Vacuum Solutions in Higher Dimensional Brans-Dicke Theory
Higher dimensional, static, cylindrically symmetric vacuum solutions with and
without a cosmological constant in the Brans-Dicke theory are presented. We
show that, for a negative cosmological constant and for specific values of the
parameters, a particular subclass of these solutions include higher dimensional
topological black hole-type solutions with a flat horizon topology. We briefly
extend our discussion to stationary vacuum and vacuum solutions.Comment: V3: Published Versio
Cylindrically symmetric, static strings with a cosmological constant in Brans-Dicke theory
The static, cylindrically symmetric vacuum solutions with a cosmological
constant in the framework of the Brans-Dicke theory are investigated. Some of
these solutions admitting Lorentz boost invariance along the symmetry axis
correspond to local, straight cosmic strings with a cosmological constant. Some
physical properties of such solutions are studied. These strings apply
attractive or repulsive forces on the test particles. A smooth matching is also
performed with a recently introduced interior thick string solution with a
cosmological constant.Comment: 8 pages, Revtex; Published versio