Fast, exact CMB power spectrum estimation for a certain class of observational strategies

We describe a class of observational strategies for probing the anisotropies in the cosmic microwave background (CMB) where the instrument scans on rings which can be combined into an n-torus, the {\em ring torus}. This class has the remarkable property that it allows exact maximum likelihood power spectrum estimation in of order $N^2$ operations (if the size of the data set is $N$) under circumstances which would previously have made this analysis intractable: correlated receiver noise, arbitrary asymmetric beam shapes and far side lobes, non-uniform distribution of integration time on the sky and partial sky coverage. This ease of computation gives us an important theoretical tool for understanding the impact of instrumental effects on CMB observables and hence for the design and analysis of the CMB observations of the future. There are members of this class which closely approximate the MAP and Planck satellite missions. We present a numerical example where we apply our ring torus methods to a simulated data set from a CMB mission covering a 20 degree patch on the sky to compute the maximum likelihood estimate of the power spectrum $C_\ell$ with unprecedented efficiency.Comment: RevTeX, 14 pages, 5 figures. A full resolution version of Figure 1 and additional materials are at http://feynman.princeton.edu/~bwandelt/RT

Strengthening impact assessment: a call for integration and focus

We suggest that the impact assessment community has lost its way based on our observation that impact assessment is under attack because of a perceived lack of efficiency. Specifically, we contend that the proliferation of different impact assessment types creates separate silos of expertise and feeds arguments for not only a lack of efficiency but also a lack of effectiveness of the process through excessive specialisation and a lack of interdisciplinary practice. We propose that the solution is a return to the basics of impact assessment with a call for increased integration around the goal of sustainable development and focus through better scoping. We rehearse and rebut counter arguments covering silo-based expertise, advocacy, democracy, sustainability understanding and communication. We call on the impact assessment community to rise to the challenge of increasing integration and focus, and to engage in the debate about the means of strengthening impact assessment

A Limit on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales

A ground-based polarimeter, PIQUE, operating at 90 GHz has set a new limit on the magnitude of any polarized anisotropy in the cosmic microwave background. The combination of the scan strategy and full width half maximum beam of 0.235 degrees gives broad window functions with average multipoles, l = 211+294-146 and l = 212+229-135 for the E- and B-mode window functions, respectively. A joint likelihood analysis yields simultaneous 95% confidence level flat band power limits of 14 and 13 microkelvin on the amplitudes of the E- and B-mode angular power spectra, respectively. Assuming no B-modes, a 95% confidence limit of 10 microkelvin is placed on the amplitude of the E-mode angular power spectrum alone.Comment: 4 pages, 3 figures, submitted to Astrophysical Journal Letter

Primordial Gravitational Wave Detectability with Deep Small-sky Cosmic Microwave Background Experiments

We use the Bayesian estimation on direct T - Q - U cosmic microwave background (CMB) polarization maps to forecast errors on the tensor-to-scalar power ratio r, and hence on primordial gravitational waves, as a function of sky coverage f_sky. This map-based likelihood filters the information in the pixel-pixel space into the optimal combinations needed for r detection for cut skies, providing enhanced information over a first-step linear separation into a combination of E, B, and mixed modes, and ignoring the latter. With current computational power and for typical resolutions appropriate for r detection, the large matrix inversions required are accurate and fast. Our simulations explore two classes of experiments, with differing bolometric detector numbers, sensitivities, and observational strategies. One is motivated by a long duration balloon experiment like Spider, with pixel noise ∝ √f_sky for a specified observing period. This analysis also applies to ground-based array experiments. We find that, in the absence of systematic effects and foregrounds, an experiment with Spider-like noise concentrating on f_sky ~ 0.02-0.2 could place a 2σ_r ≈ 0.014 boundary (~95% confidence level), which rises to 0.02 with an ℓ-dependent foreground residual left over from an assumed efficient component separation. We contrast this with a Planck-like fixed instrumental noise as f_sky varies, which gives a Galaxy-masked (f_sky = 0.75) 2σ_r ≈ 0.015, rising to ≈0.05 with the foreground residuals. Using as the figure of merit the (marginalized) one-dimensional Shannon entropy of r, taken relative to the first 2003 WMAP CMB-only constraint, gives –2.7 bits from the 2012 WMAP9+ACT+SPT+LSS data, and forecasts of –6 bits from Spider (+ Planck); this compares with up to –11 bits for CMBPol, COrE, and PIXIE post-Planck satellites and –13 bits for a perfectly noiseless cosmic variance limited experiment. We thus confirm the wisdom of the current strategy for r detection of deeply probed patches covering the f_sky minimum-error trough with balloon and ground experiments

Observational Constraints on Visser's Cosmological Model

Theories of gravity for which gravitons can be treated as massive particles have presently been studied as realistic modifications of General Relativity, and can be tested with cosmological observations. In this work, we study the ability of a recently proposed theory with massive gravitons, the so-called Visser theory, to explain the measurements of luminosity distance from the Union2 compilation, the most recent Type-Ia Supernovae (SNe Ia) dataset, adopting the current ratio of the total density of non-relativistic matter to the critical density ($\Omega_m$) as a free parameter. We also combine the SNe Ia data with constraints from Baryon Acoustic Oscillations (BAO) and CMB measurements. We find that, for the allowed interval of values for $\Omega_m$, a model based on Visser's theory can produce an accelerated expansion period without any dark energy component, but the combined analysis (SNe Ia + BAO + CMB) shows that the model is disfavored when compared with $\Lambda$CDM model.Comment: 6 pages, 4 figure

Exactly solvable model of A + A \to 0 reactions on a heterogeneous catalytic chain

We present an exact solution describing equilibrium properties of the catalytically-activated A + A \to 0 reaction taking place on a one-dimensional lattice, where some of the sites possess special "catalytic" properties. The A particles undergo continuous exchanges with the vapor phase; two neighboring adsorbed As react when at least one of them resides on a catalytic site (CS). We consider three situations for the CS distribution: regular, annealed random and quenched random. For all three CS distribution types, we derive exact results for the disorder-averaged pressure and present exact asymptotic expressions for the particles' mean density. The model studied here furnishes another example of a 1D Ising-type system with random multi-site interactions which admits an exact solution.Comment: 7 pages, 3 Figures, appearing in Europhysics Letter

Improving the Prospects for Detecting Extrasolar Planets in Gravitational Microlensing in 2002

Gravitational microlensing events of high magnification have been shown to be promising targets for detecting extrasolar planets. However, only a few events of high magnification have been found using conventional survey techniques. Here we demonstrate that high magnification events can be readily found in microlensing surveys using a strategy that combines high frequency sampling of target fields with online difference imaging analysis. We present 10 microlensing events with peak magnifications greater than 40 that were detected in real-time towards the Galactic Bulge during 2001 by MOA. We show that Earth mass planets can be detected in future events such as these through intensive follow-up observations around the event peaks. We report this result with urgency as a similar number of such events are expected in 2002.Comment: 11 pages, 3 embedded ps figures including 2 colour, revised version accepted by MNRA

Observational constraints on modified gravity models and the Poincar\'e dodecahedral topology

We study the constraints that spatial topology may place on the parameters of models that account for the accelerated expansion of the universe via infrared modifications to general relativity, namely the Dvali-Gabadadze-Porrati braneworld model as well as the Dvali-Turner and Cardassian models. By considering the Poincar\'e dodecahedral space as the circles-in-the-sky observable spatial topology, we examine the constraints that can be placed on the parameters of each model using type Ia supernovae data together with the baryon acoustic peak in the large scale correlation function of the Sloan Digital Sky Survey of luminous red galaxies and the Cosmic Microwave Background Radiation shift parameter data. We show that knowledge of spatial topology does provide relevant constraints, particularly on the curvature parameter, for all models.Comment: Revtex4, 10 pages, 1 table, 12 figures; version to match the one to be published in Physical Review

Weak Lensing Reconstruction and Power Spectrum Estimation: Minimum Variance Methods

Large-scale structure distorts the images of background galaxies, which allows one to measure directly the projected distribution of dark matter in the universe and determine its power spectrum. Here we address the question of how to extract this information from the observations. We derive minimum variance estimators for projected density reconstruction and its power spectrum and apply them to simulated data sets, showing that they give a good agreement with the theoretical minimum variance expectations. The same estimator can also be applied to the cluster reconstruction, where it remains a useful reconstruction technique, although it is no longer optimal for every application. The method can be generalized to include nonlinear cluster reconstruction and photometric information on redshifts of background galaxies in the analysis. We also address the question of how to obtain directly the 3-d power spectrum from the weak lensing data. We derive a minimum variance quadratic estimator, which maximizes the likelihood function for the 3-d power spectrum and can be computed either from the measurements directly or from the 2-d power spectrum. The estimator correctly propagates the errors and provides a full correlation matrix of the estimates. It can be generalized to the case where redshift distribution depends on the galaxy photometric properties, which allows one to measure both the 3-d power spectrum and its time evolution.Comment: revised version, 36 pages, AAS LateX, submitted to Ap

Design guide for high pressure oxygen systems

A repository for critical and important detailed design data and information, hitherto unpublished, along with significant data on oxygen reactivity phenomena with metallic and nonmetallic materials in moderate to very high pressure environments is documented. This data and information provide a ready and easy to use reference for the guidance of designers of propulsion, power, and life support systems for use in space flight. The document is also applicable to designs for industrial and civilian uses of high pressure oxygen systems. The information presented herein are derived from data and design practices involving oxygen usage at pressures ranging from about 20 psia to 8000 psia equal with thermal conditions ranging from room temperatures up to 500 F