33 research outputs found
Radiative fields in spacetimes with Minkowski and de Sitter asymptotics
The classical Bondi-Penrose approach to the gravitational radiation theory in
asymptotically flat spacetimes is recalled and recent advances in the proofs of
the existence of such spacetimes are briefly reviewed. We then mention the
unique role of the boost-rotation symmetric spacetimes, representing uniformly
accelerated objects, as the only explicit radiative solutions known which are
asymptotically flat; they are used as test beds in numerical relativity and
approximation methods.
The main part of the review is devoted to the examples of radiative fields in
the vacuum spacetimes with positive cosmological constant. Type N solutions are
analyzed by using the equation of geodesic deviation. Both these and
Robinson-Trautman solutions of type II are shown to approach de Sitter universe
asymptotically. Recent work on the the radiative fields due to uniformly
accelerated charges in de Sitter spacetime ("cosmological Born's solutions") is
reviewed and the properties of these fields are discussed with a perspective to
characterize general features of radiative fields near a de Sitter-like
infinity.Comment: 23 pages, invited talk, 10th Greek Relativity Meeting, Chalkidiki,
May 200
Charged particle in higher dimensional weakly charged rotating black hole spacetime
We study charged particle motion in weakly charged higher dimensional black
holes. To describe the electromagnetic field we use a test field approximation
and use the higher dimensional Kerr-NUT-(A)dS metric as a background geometry.
It is shown that for a special configuration of the electromagnetic field the
equations of motion of charged particles are completely integrable. The vector
potential of such a field is proportional to one of the Killing vectors (called
primary Killing vector) from the `Killing tower' of symmetry generating objects
which exists in the background geometry. A free constant in the definition of
the adopted electromagnetic potential is proportional to the electric charge of
the higher dimensional black hole. The full set of independent conserved
quantities in involution is found. It is demonstrated, that Hamilton-Jacobi
equations are separable, as well as the corresponding Klein-Gordon equation and
its symmetry operators.Comment: 9 pages, no figure
Weakly charged generalized Kerr-NUT-(A)dS spacetimes
We find an explicit solution of the source free Maxwell equations in a
generalized Kerr-NUT-(A)dS spacetime in all dimensions. This solution is
obtained as a linear combination of the closed conformal Killing-Yano tensor
, which is present in such a spacetime, and a derivative of the primary
Killing vector, associated with . For the vanishing cosmological
constant the obtained solution reduces to the Wald's electromagnetic field
generated from the primary Killing vector.Comment: 4 pages, no figures v2: added reference
Geometry of Lax pairs: particle motion and Killing-Yano tensors
A geometric formulation of the Lax pair equation on a curved manifold is
studied using phase space formalism. The corresponding (covariantly conserved)
Lax tensor is defined and the method of generation of constants of motion from
it is discussed. It is shown that when the Hamilton equations of motion are
used, the conservation of the Lax tensor translates directly to the well known
Lax pair equation, with one matrix identified with components of the Lax tensor
and the other matrix constructed from the (metric) connection. A generalization
to Clifford objects is also discussed. Nontrivial examples of Lax tensors for
geodesic and charged particle motion are found in spacetimes admitting hidden
symmetry of Killing--Yano tensors.Comment: 13 pages, 1 figur
Electron in higher-dimensional weakly charged rotating black hole spacetimes
We demonstrate separability of the Dirac equation in weakly charged rotating
black hole spacetimes in all dimensions. The electromagnetic field of the black
hole is described by a test field approximation, with vector potential
proportional to the primary Killing vector field. It is shown that the
demonstrated separability can be intrinsically characterized by the existence
of a complete set of mutually commuting first order symmetry operators
generated from the principal Killing-Yano tensor. The presented results
generalize the results on integrability of charged particle motion and
separability of charged scalar field studied in [1].Comment: 12 pages, no figure
Ring wormholes and time machines
In the present paper we discuss properties of a model of a ring wormhole,
recently proposed by Gibbons and Volkov. Such a wormhole connects two flat
spacetimes which are glued through discs of the radius bounded by the
string with negative angle deficit . The presence of the string's matter
violating null energy condition makes the wormhole static and traversable. We
study gravitational field of static sources in such a spacetime in the weak
field approximation. In particular, we discuss how a field of an oblate thin
massive shell surrounding one of the wormhole's mouth is modified by its
presence. We also obtain a solution of a similar problem when both mouths of
the wormhole are located in the same space. This approximate solution if found
for the case when the distance between these mouths is much larger than the
radius of the ring. We demonstrate that the corresponding locally static
gravitational field in such a multiply connected space is non-potential. As a
result of this, the proper time gap for the clock's synchronization linearly
grows with time and closed timelike curves are formed. This process inevitably
transforms such a traversable ring wormhole into a time machine. We estimate
the time scale of this process.Comment: 23 pages, 19 figure
Hydrolysis of PLA-like Plasma Polymer Films with Varying Degree of Crosslinking
Poly-lactide acid (PLA) based biodegradable films are of interest for packaging materials or bioapplications. Plasma-assisted vacuum evaporation technique uses oligomers released during thermal decomposition of source polymer as precursors for plasma polymerization. Conventionally prepared PLA with mw = 10000 g/mol was used as a source polymer. Films were prepared at various RF (13.56 MHz) plasma powers (0-20 W) in order to vary the amount of crosslinking in the film.Swelling and hydrolysis of films were monitored in real time using spectroscopic ellipsometry. The concentration profile of products of hydrolysis was measured by liquid-chromatography (LC-MS). FTIR, XPS and SEM analyses were used for monitoring of film composition and surface characterization. Molecular weights of source polymer and of the plasma polymer were determined by gel-permeation chromatography (GPC). Possibility to prepare PLA-like plasma polymer films with controlled degradability by hydrolysis was demonstrated
Interpreting the C-metric
The basic properties of the C-metric are well known. It describes a pair of causally
separated black holes which accelerate in opposite directions under the action of
forces represented by conical singularities. However, these properties can be demonstrated
much more transparently by making use of recently developed coordinate
systems for which the metric functions have a simple factor structure. These enable
us to obtain explicit Kruskal–Szekeres-type extensions through the horizons and
construct two-dimensional conformal Penrose diagrams. We then combine these
into a three-dimensional picture which illustrates the global causal structure of the
space-time outside the black hole horizons. Using both the weak field limit and
some invariant quantities, we give a direct physical interpretation of the parameters
which appear in the new form of the metric. For completeness, relations to other
familiar coordinate systems are also discussed