Cosmic Rulers

We derive general covariant expressions for the six independent observable modes of distortion of ideal standard rulers in a perturbed Friedmann-Robertson-Walker spacetime. Our expressions are gauge-invariant and valid on the full sky. These six modes are most naturally classified in terms of their rotational properties on the sphere, yielding two scalars, two vector (spin-1), and two tensor (spin-2) components. One scalar corresponds to the magnification, while the spin-2 components correspond to the shear. The vector components allow for a polar/axial decomposition analogous to the E/B-decomposition for the shear. Scalar modes do not contribute to the axial (B-)vector, opening a new avenue to probing tensor modes. Our results apply, but are not limited to, the distortion of correlation functions (of the CMB, 21cm emission, or galaxies) as well as to weak lensing shear and magnification, all of which can be seen as methods relying on "standard rulers".Comment: 31 pages, 3 figures (v3); v2: minor changes reflecting PRD published version; v3: evolving ruler case relegated to arXiv:1305.1299, added proper time condition for observer, additional test cases for magnificatio

Delayed Recombination and Standard Rulers

Measurements of Baryonic Acoustic Oscillations in galaxy surveys have been recognized as a powerful tool for constraining dark energy. However, this method relies on the knowledge of the size of the acoustic horizon at recombination derived from Cosmic Microwave Background Anisotropy measurements. This estimate is typically derived assuming a standard recombination scheme; additional radiation sources can delay recombination altering the cosmic ionization history and the cosmological inferences drawn from CMB and BAO data. In this paper we quantify the effect of delayed recombination on the determination of dark energy parameters from future BAO surveys such as BOSS and WFMOS. We find the impact to be small but still not negligible. In particular, if recombination is non-standard (to a level still allowed by CMB data), but this is ignored, future surveys may incorrectly suggest the presence of a redshift dependent dark energy component. On the other hand, in the case of delayed recombination, adding to the analysis one extra parameter describing deviations from standard recombination, does not significantly degrade the error-bars on dark energy parameters and yields unbiased estimates.Comment: 8 pages, 5 figure

Interstate competition and political stability

Previous theories of globalization have examined factor mobility’s effect on the political conflict between social classes. But factor mobility also increases competition between state rulers in provid- ing services for citizens. I ask how this interstate competition affects the process of political change. In a simple model, interstate competition substitutes for democracy, by forcing rulers to invest in pub- lic goods so as to avoid capital and labor leaving the country. As a result, citizens are less willing to struggle for democracy, and rulers are less willing to oppose it, when interstate competition is strong. Therefore, there is less conflict over the level of democracy. The theory is tested on a post-war panel of countries, using neighboring countries’ financial openness as a proxy for factor mobility. As the theory predicts, states experience fewer changes in their level of democracy when their neighbors are financially open

Coherent Superposition States as Quantum Rulers

We explore the sensitivity of an interferometer based on a quantum circuit for coherent states. We show that its sensitivity is at the Heisenberg limit. Moreover we show that this arrangement can measure very small length intervals