38,322 research outputs found
Exact impulsive gravitational waves in spacetimes of constant curvature
Exact solutions exist which describe impulsive gravitational waves
propagating in Minkowski, de Sitter, or anti-de Sitter universes. These may be
either nonexpanding or expanding. Both cases in each background are reviewed
here from a unified point of view. All the main methods for their construction
are described systematically: the Penrose "cut and paste" method, explicit
construction of continuous coordinates, distributional limits of sandwich
waves, embedding from higher dimensions, and boosts of sources or limits of
infinite accelerations.
Attention is concentrated on the most interesting specific solutions. In
particular, the nonexpanding impulsive waves that are generated by null
multipole particles are described. These generalize the well-known
Aichelburg-Sexl and Hotta-Tanaka monopole solutions. Also described are the
expanding spherical impulses that are generated by snapping and colliding
strings. Geodesics and some other properties of impulsive wave spacetimes are
also summarized.Comment: 33 pages, LaTeX 2e, in Gravitation: Following the Prague Inspiration
(To celebrate the 60th birthday of Jiri Bicak), O.Semerak, J.Podolsky,
M.Zofka (eds.), World Scientific, Singapore, to appear in 2002, pp 205-24
Accelerated Universe from Gravity Leaking to Extra Dimensions
We discuss the idea that the accelerated Universe could be the result of the
gravitational leakage into extra dimensions on Hubble distances rather than the
consequence of non-zero cosmological constant.Comment: 20 pages, 6 figure
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