Nucleation of vacuum phase transitions by topological defects

The Euclidean action is calculated in the thin-wall approximation for a first-order vacuum phase transition in which the bubble appears symmetrically around either a global monopole or a gauge cosmic string. The bubble is assumed to be much larger than the core size of the monopole or string. In both cases the value of the Euclidean action is shown to be reduced below the $O(4)$ symmetric action value, indicating that the topological defects act as effective nucleation sites for vacuum decay.Comment: 10 pages, LaTe

From Wormholes to the Warp Drive: Using theoretical physics to place ultimate bounds on technology

The serious study of such science fiction staples as wormholes, time travel, and the warp drive, as a means of understanding and constraining possible realistic solutions within General Relativity is reviewed.Comment: 10 pages LaTeX; to appear in Phi Kappa Phi Foru

Scientific divers quantify first known outbreaks of cold-water coral disease

Coral diseases are widely reported in the tropics but the first incidence of cold-water coral disease was not noted until 2002 when divers recorded an outbreak at 10-28 m depth off Lundy in a NE Atlantic marine protected area. The seafan Eunicella verrucosa exhibited coenchyme necrosis and subsequent diving surveys of \u3e600 colonies at 13 sites since revealed that disease outbreaks were widespread in SW England to depths of 50 m from 2003-2008, possibly caused by infection by Vibrio bacteria at high temperatures

Experimental evaluation of Kuhn's geometric index of reduction and the flat-flake problem

This paper presents the results of an experiment designed to explore the performance of Kuhn's Geometric Index of Unifacial Reduction [S. Kuhn, A geometric index of reduction for unifacial stone tools, Journal of Archaeological Science 17 (1990) 585-593] in measuring the amount of material removed over a sequence of retouching events for a population of 30 flakes. The index provides a reliable absolute measure of reduction under experimental conditions, and does so irrespective of blank cross-section, suggesting that the "flat-flake" problem is not necessarily a serious difficulty for the index. Furthermore, Kuhn's Index provided a more sensitive and robust measurement of the extent of reduction than any of the alternative techniques proposed in recent years

Radiation flux and spectrum in the Vaidya collapse model

We consider the quantization of a massless scalar field, using the geometric optics approximation, in the background spacetime of a collapsing spherical self-similar Vaidya star, which forms a black hole or a naked singularity. We show that the outgoing radiation flux of the quantized scalar field diverges on the Cauchy horizon. The spectrum of the produced scalar partcles is non-thermal when the background develops a naked singularity. These results are analogous to those obtained for the scalar quantization on a self-similar dust cloud.Comment: 10 pages, Latex Fil

First order and stable relativistic dissipative hydrodynamics

Relativistic thermodynamics is derived from kinetic equilibrium in a general frame. Based on a novel interpretation of Lagrange multipliers in the equilibrium state we obtain a generic stable but first order relativistic dissipative hydrodynamics. Although this was believed to be impossible, we circumvent this difficulty by a specific handling of the heat flow.Comment: revised, 11 pages, accepted for publication in PL

Semiclassical Effects Induced by Aharonov-Bohm Interaction Between a Cosmic String and a Scalar Field

In the context of the vacuum polarization effect, we consider the backreaction of the energy-momentum tensor of a charged scalar field on the background metric of a cosmic string carrying a magnetic flux $\Phi$. Working within the semiclassical approach to the Einstein eqs. we find the first-order (in $\hbar$) metric associated to the magnetic flux cosmic string. We show that the contribution to the vacuum polarization effect coming from the Aharonov-Bohm interaction is larger than the one coming from the non-trivial gravitational interaction.Comment: 13 pages, no figures, accepted for publication in Phys. Letters

Zero temperature black holes in semiclassical gravity

The semiclassical Einstein equations are solved to first order in $\epsilon = \hbar/M^2$ for the case of an extreme or nearly extreme Reissner-Nordstr\"{o}m black hole perturbed by the vacuum stress-energy of quantized free fields. It is shown that, for realistic fields of spin 0, 1/2, or 1, any zero temperature black hole solution to the equations must have an event horizon at $r_h < |Q|$, with $Q$ the charge of the black hole. It is further shown that no black hole solutions with $r_h < |Q|$ can be obtained by solving the semiclassical Einstein equations perturbatively.Comment: 7 pages, to appear in the Proceedings of the Ninth Marcel Grossmann Meeting, change in titl