20 research outputs found
Radiation generated by accelerating and rotating charged black holes in (anti-)de Sitter space
Asymptotic behaviour of gravitational and electromagnetic fields of exact
type D solutions from the large Plebanski-Demianski family of black hole
spacetimes is analyzed. The amplitude and directional structure of radiation is
evaluated in cases when the cosmological constant is non-vanishing, so that the
conformal infinities have either de Sitter-like or anti-de Sitter-like
character. In particular, explicit relations between the parameters that
characterize the sources (that is their mass, electric and magnetic charges,
NUT parameter, rotational parameter, and acceleration) and properties of the
radiation generated by them are presented. The results further elucidate the
physical interpretation of these solutions and may help to understand radiative
characteristics of more general spacetimes than those that are asymptotically
flat.Comment: 24 pages, 18 figures. To appear in Classical and Quantum Gravit
Gyratons on Melvin spacetime
We present and analyze new exact gyraton solutions of algebraic type II on a
background which is static, cylindrically symmetric Melvin universe of type D.
For a vanishing electromagnetic field it reduces to previously studied gyratons
on Minkowski background. We demonstrate that the solutions are member of a more
general family of the Kundt spacetimes. We show that the Einstein equations
reduce to a set of mostly linear equations on a transverse 2-space and we
discuss the properties of polynomial scalar curvature invariants which are
generally non-constant but unaffected by the presence of gyratons.Comment: 15 pages, no figures, journal version extended by appendices B and
Higher-dimensional Kundt waves and gyratons
We present and analyze exact solutions of the Einstein-Maxwell equations in
higher dimensions which form a large subclass of the Kundt family of
spacetimes. We assume that the cosmological constant may be nonvanishing, and
the matter consists of a background aligned electromagnetic field and an
additional pure radiation (gyratonic) field with a spin. We show that the field
equations reduce to a set of linear equations on the transverse space which can
be solved exactly and expressed in terms of the Green functions. We thus find
explicit exact gyratonic gravitational and electromagnetic fields created by a
radiation beam of null matter with arbitrary profiles of energy density and
angular momenta. In the absence of the gyratonic matter we obtain pure
nonexpanding higher-dimensional gravitational waves.
In particular, we investigate gyratons and waves propagating on backgrounds
which are a direct-product of 2-spaces of constant curvature. Such type D or 0
background spacetimes generalize 4-dimensional Nariai, anti-Nariai and
Plebanski-Hacyan universes, and conformally flat Bertotti-Robinson and
Minkowski spaces. These spacetimes belong to a wider class of spaces which
admit the Kahler structure related to the background magnetic field. The
obtained wave and gyraton solutions are also members of the recently discussed
class of spacetimes with constant scalar invariants (CSI) of the curvature
tensor.Comment: 18 pages, no figure
Electromagnetic solitons in quantum vacuum
In the limit of extremely intense electromagnetic fields the Maxwell equations are modified due to the photon-photon scattering that makes the vacuum refraction index depend on the field amplitude. In the presence of electromagnetic waves with small but finite wave numbers the vacuum behaves as a dispersive medium. We show that the interplay between the vacuum polarization and the nonlinear effects in the interaction of counter-propagating electromagnetic waves can result in the formation of Kadomtsev-Petviashvily solitons and, in one-dimension configuration, of Korteveg-de-Vries type solitons that can propagate over a large distance without changing their shape
Safety of Statin Pretreatment in Intravenous Thrombolysis for Acute Ischemic Stroke
Background and Purpose-A recent meta-analysis investigating the association between statins and early outcomes in acute ischemic stroke (AIS) patients treated with intravenous thrombolysis (IVT) indicated that prestroke statin treatment was associated with increased risk of 90-day mortality and symptomatic intracranial hemorrhage. We investigated the potential association of statin pretreatment with early outcomes in a large, international registry of AIS patients treated with IVT