Tunneling with negative tension

We describe a new family of thin-wall instantons, with negative tension bubble walls, that mediate tunneling between Minkowski or de Sitter vacua. Some of these instantons can have exponentially enhanced tunneling rates, and would dominate the Euclidean path integral, representing a severe non-perturbative instability in any theory which supports them. We give two constructions of these instantons in theories which are perturbatively stable, but violate the null energy condition. One construction uses a scalar field theory with higher-derivative kinetic term, and is similar to the Coleman-de Luccia positive tension instanton. The other construction employs a negative-tension boundary arising from Z_2 orbifolding: it resembles a "bubble of nothing" which nucleates and grows, consuming the surrounding de Sitter or Minkowski spacetime. We explain how the spectral flow for fluctutations about the thin-wall tunneling solutions automatically protects causality, for both positive and negative tension instantons. We comment briefly on the relation of these solutions to a Kalzua-Klein "bubble of nothing," cosmological models relying on ghost condensates, and string theory orientifolds.Comment: PDFLaTeX, 43pp v2: new appendix, references adde

Moments of inertia of several airplanes

This paper, which is the first of a series presenting the results of such measurements, gives the momental ellipsoids of ten army and naval biplanes and one commercial monoplane. The data were obtained by the use of a pendulum method, previously described. The moments of inertia are expressed in coefficient as well as in dimensional form, so that those for airplanes of widely different weights and dimensions can be compared

Los restos de las carabelas de Vicente Yáñez Pinzón, de 1500

Págs. 169-177 ; mapas

In the wake of public crises, political “blame games” can lead to bad public policies

When things go wrong, such as when disasters and other crises occur, politicians often look to assign blame in order to gain political capital. But how do members of the public react when politicians and public servants apportion blame? Using the April 2013 Boston Marathon bombings as a case study, John Marvel finds that an individual’s sense of who is to blame depends on who is doing the blaming, and who is being blamed. He argues that such ‘blame games’ can have an effect on which government policy responses people are willing to support to address future crises