Cosmological Parameters from CMB Maps without Likelihood Approximation

We propose an efficient Bayesian MCMC algorithm for estimating cosmological parameters from CMB data without use of likelihood approximations. It builds on a previously developed Gibbs sampling framework that allows for exploration of the joint CMB sky signal and power spectrum posterior, P(s,Cl|d), and addresses a long-standing problem of efficient parameter estimation simultaneously in high and low signal-to-noise regimes. To achieve this, our new algorithm introduces a joint Markov Chain move in which both the signal map and power spectrum are synchronously modified, by rescaling the map according to the proposed power spectrum before evaluating the Metropolis-Hastings accept probability. Such a move was already introduced by Jewell et al. (2009), who used it to explore low signal-to-noise posteriors. However, they also found that the same algorithm is inefficient in the high signal-to-noise regime, since a brute-force rescaling operation does not account for phase information. This problem is mitigated in the new algorithm by subtracting the Wiener filter mean field from the proposed map prior to rescaling, leaving high signal-to-noise information invariant in the joint step, and effectively only rescaling the low signal-to-noise component. To explore the full posterior, the new joint move is then interleaved with a standard conditional Gibbs sky map move. We apply our new algorithm to simplified simulations for which we can evaluate the exact posterior to study both its accuracy and performance, and find good agreement with the exact posterior; marginal means agree to less than 0.006 sigma, and standard deviations to better than 3%. The Markov Chain correlation length is of the same order of magnitude as those obtained by other standard samplers in the field.Comment: 9 pages, 3 figures, Published in Ap

Robust numerical computation of the 3D scalar potential field of the cubic Galileon gravity model at solar system scales

Direct detection of dark energy or modified gravity may finally be within reach due to ultrasensitive instrumentation such as atom interferometry capable of detecting incredibly small scale accelerations. Forecasts, constraints and measurement bounds can now too perhaps be estimated from accurate numerical simulations of the fifth force and its Laplacian field at solar system scales. The cubic Galileon gravity scalar field model (CGG), which derives from the DGP braneworld model, describes modified gravity incorporating a Vainshtein screening mechanism. The nonlinear derivative interactions in the CGG equation suppress the field near regions of high density, thereby restoring general relativity (GR) while far from such regions, field enhancement is comparable to GR and the equation is dominated by a linear term. This feature of the governing PDE poses some numerical challenges for computation of the scalar potential, force and Laplacian fields even under stationary conditions. Here we present a numerical method based on finite differences for solution of the static CGG scalar field for a 2D axisymmetric Sun-Earth system and a 3D Cartesian Sun-Earth-Moon system. The method relies on gradient descent of an integrated residual based on the normal attractive branch of the CGG equation. The algorithm is shown to be stable, accurate and rapidly convergent toward the global minimum state. We hope this numerical study, which can easily be extended to include smaller bodies such as detection satellites, will prove useful to future measurement of modified gravity force fields at solar system scales

Dual Purpose Lyot Coronagraph Masks for Simultaneous High-Contrast Imaging and High-Resolution Wavefront Sensing

Directly imaging Earth-sized exoplanets with a visible-light coronagraph instrument on a space telescope will require a system that can achieve $\sim10^{-10}$ raw contrast and maintain it for the duration of observations (on the order of hours or more). We are designing, manufacturing, and testing Dual Purpose Lyot coronagraph (DPLC) masks that allow for simultaneous wavefront sensing and control using out-of-band light to maintain high contrast in the science focal plane. Our initial design uses a tiered metallic focal plane occulter to suppress starlight in the transmitted coronagraph channel and a dichroic-coated substrate to reflect out-of-band light to a wavefront sensing camera. The occulter design introduces a phase shift such that the reflected channel is a Zernike wavefront sensor. The dichroic coating allows higher-order wavefront errors to be detected which is especially critical for compensating for residual drifts from an actively-controlled segmented primary mirror. A second-generation design concept includes a metasurface to create polarization-dependent phase shifts in the reflected beam, which has several advantages including an extended dynamic range. We will present the focal plane mask designs, characterization, and initial testing at NASA's High Contrast Imaging Testbed (HCIT) facility.Comment: To appear in the Proceedings of the SPIE, Techniques and Instrumentation for Detection of Exoplanets X

Data processing for high-contrast imaging with the James Webb Space Telescope

The JamesWebb Space Telescope (JWST) will probe circumstellar environments at an unprecedented sensitivity. However, the performance of high-contrast imaging instruments is limited by the residual light from the star at close separations (<2-3"), where the incidence of exoplanets increases rapidly. There is currently no solution to get rid of the residual starlight down to the photon noise level at those separations, which may prevent some crucial discoveries. JWST's launch is planned for October 2021 with a planned baseline science mission lifetime of only five years. Thus, it is crucial to start developing a solution to this problem before its launch. We are investigating an innovative approach of post-processing built on a Bayesian framework that provides a more robust determination of faint astrophysical structures around a bright source. This approach uses a model of high-contrast imaging instrument that takes advantage of prior information, such as data from wavefront sensing (WFS) operations on JWST, to estimate simultaneously instrumental aberrations and the circumstellar environment. With this approach, our goal is to further improve the contrast gain over the contrast that can be achieved with JWST instruments, starting with NIRCam direct imaging and coronagraphic imaging. This work will pave the way for the future space-based high-contrast imaging instruments such as the Nancy Grace Roman Space Telescope_ Coronagraph Instrument (Roman CGI). This technique will be crucial to make the best use of the telemetry data that will be collected during the CGI operations

Analysis of WMAP 7-year Temperature Data: Astrophysics of the Galactic Haze

We analyse WMAP 7-year temperature data, jointly modeling the cosmic microwave background (CMB) and Galactic foreground emission. We use the Commander code based on Gibbs sampling. Thus, from the WMAP7 data, we derive simultaneously the CMB and Galactic components on scales larger than 1deg with sensitivity improved relative to previous work. We conduct a detailed study of the low-frequency foreground with particular focus on the "microwave haze" emission around the Galactic center. We demonstrate improved performance in quantifying the diffuse galactic emission when Haslam 408MHz data are included together with WMAP7, and the spinning and thermal dust emission is modeled jointly. We also address the question of whether the hypothetical galactic haze can be explained by a spatial variation of the synchrotron spectral index. The excess of emission around the Galactic center appears stable with respect to variations of the foreground model that we study. Our results demonstrate that the new galactic foreground component - the microwave haze - is indeed present.Comment: 16 pages, 16 figures, Published on Ap

International films and international markets: the globalisation of Hollywood entertainment, c.1921-1951

The international appeal of Hollywood films through the twentieth century has been a subject of interest to economic and film historians alike. This paper employs some of the methods of the economic historian to evaluate key arguments within the film history literature explaining the global success of American films. Through careful analysis of both existing and newly constructed data sets, the paper examines the extent to which Hollywood's foreign earnings were affected by: film production costs; the extent of global distribution networks; and also the international orientation of the films themselves. The paper finds that these factors influenced foreign earnings in quite distinct ways, and that their relative importance changed over time. The evidence presented here suggests a degree of interaction between the production and distribution arms of the major US film companies in their pursuit of foreign markets that would benefit from further archival-based investigation

A CMB Gibbs sampler for localized secondary anisotropies

As well as primary fluctuations, CMB temperature maps contain a wealth of additional information in the form of secondary anisotropies. Secondary effects that can be identified with individual objects, such as the thermal and kinetic Sunyaev-Zel'dovich (SZ) effects due to galaxy clusters, are difficult to unambiguously disentangle from foreground contamination and the primary CMB however. We develop a Bayesian formalism for rigorously characterising anisotropies that are localised on the sky, taking the TSZ and KSZ effects as an example. Using a Gibbs sampling scheme, we are able to efficiently sample from the joint posterior distribution for a multi-component model of the sky with many thousands of correlated physical parameters. The posterior can then be exactly marginalised to estimate properties of the secondary anisotropies, fully taking into account degeneracies with the other signals in the CMB map. We show that this method is computationally tractable using a simple implementation based on the existing Commander component separation code, and also discuss how other types of secondary anisotropy can be accommodated within our framework

Genetic effects on gene expression across human tissues

Characterization of the molecular function of the human genome and its variation across individuals is essential for identifying the cellular mechanisms that underlie human genetic traits and diseases. The Genotype-Tissue Expression (GTEx) project aims to characterize variation in gene expression levels across individuals and diverse tissues of the human body, many of which are not easily accessible. Here we describe genetic effects on gene expression levels across 44 human tissues. We find that local genetic variation affects gene expression levels for the majority of genes, and we further identify inter-chromosomal genetic effects for 93 genes and 112 loci. On the basis of the identified genetic effects, we characterize patterns of tissue specificity, compare local and distal effects, and evaluate the functional properties of the genetic effects. We also demonstrate that multi-tissue, multi-individual data can be used to identify genes and pathways affected by human disease-associated variation, enabling a mechanistic interpretation of gene regulation and the genetic basis of diseas