Kaluza-Klein Vortices

We study static vortex type solutions of pure gravity for $D \geq 4+1$. Non-singular vortex solutions can be obtained by considering periodic Kaluza-Klein monopoles. We also show that away from the center of the vortices the space is described by the gravitational instantons derived from minimal surfaces.Comment: 9 pages, typos corrected, to appear in JHE

Phase Transition in Compact QED(3) and the Josephson Junction

We study the finite temperature phase transition in 2+1 dimensional compact QED and its dual theory: Josephson junction. Duality of these theories at zero temperature was established long time ago by Hosotani. Phase transition in compact QED is well studied and we employ the `duality' to study the superconductivity phase transition in a Josephson junction. For a thick junction we obtain a critical temperature in terms of the geometrical properties of the junction.Comment: 9 pages, discussion added about the role of the solitons. To appear in JHE

Instabilities and the null energy condition

We show that violation of the null energy condition implies instability in a broad class of models, including classical gauge theories with scalar and fermionic matter as well as any perfect fluid. When applied to the dark energy, our results imply that $w = p / \rho$ is unlikely to be less than -1.Comment: 5 pages, 1 figure, revtex, presentation improved, minor change