239 research outputs found
Geodesic Properties and Orbits in 5-dimensional Hypercylindrical Spacetime
We investigate the geodesic motions of a massive particle and light ray in
the hyperplane orthogonal to the symmetry axis in the 5-dimensional
hypercylindrical spacetime. The class of the solutions depends on one constant
a which is the ratio of string mass density and tension. There exist unstable
orbits in null geodesic only in some range of a. The innermost stable circular
orbits in timelike geodesic also exist only in a certain range of the parameter
a. The capture cross section and the deflection angle of light ray are also
computed.Comment: 17 pages, 10 figures, 4 tables, minor corrected and reference adde
Dynamics of false vacuum bubbles with nonminimal coupling
We study the dynamics of false vacuum bubbles. A nonminimally coupled scalar
field gives rise to the effect of negative tension. The mass of a false vacuum
bubble from outside observer's point of view can be positive, zero, or
negative. The interior false vacuum has de Sitter geometry, while the exterior
true vacuum background can have geometry depending on the vacuum energy. We
show that there exist expanding false vacuum bubbles without the initial
singularity in the past.Comment: 17 pages, 13 figure
- …