Generalized Slow Roll for Large Power Spectrum Features

We develop a variant of the generalized slow roll approach for calculating the curvature power spectrum that is well-suited for order unity deviations in power caused by sharp features in the inflaton potential. As an example, we show that predictions for a step function potential, which has been proposed to explain order unity glitches in the CMB temperature power spectrum at multipoles l=20-40, are accurate at the percent level. Our analysis shows that to good approximation there is a single source function that is responsible for observable features and that this function is simply related to the local slope and curvature of the inflaton potential. These properties should make the generalized slow roll approximation useful for inflation-model independent studies of features, both large and small, in the observable power spectra.Comment: 13 pages, 21 figures, submitted to Phys. Rev.

Evolution of the gas mass fraction in galaxy clusters

The mass fraction of hot gas in clusters is a basic quantity whose level and dependence on the cluster mass and redshift are intimately linked to all cluster X-ray and SZ measures. Modeling the evolution of the gas fraction is clearly a necessary ingredient in the description of the hierarchical growth of clusters through mergers of subclumps and mass accretion on the one hand, and the dispersal of gas from the cluster galaxies by tidal interactions, galactic winds, and ram pressure stripping on the other hand. A reasonably complete description of this evolution can only be given by very detailed hydrodynamical simulations, which are, however, resource-intensive, and difficult to implement in the mapping of parameter space. A much more practical approach is the use of semi-analytic modeling that can be easily implemented to explore a wide range of parameters. We present first results from a simple model that describes the build up of the gas mass fraction in clusters by following the overall impact of the above processes during the merger and accretion history of each cluster in the ensemble. Acceptable ranges for model parameters are deduced through comparison with results of X-ray observations. Basic implications of our work for modeling cluster statistical properties, and the use of these properties in joint cosmological data analyses, are discussed.Comment: 10 pages, 6 figures, updated to match MNRAS accepted versio

Cosmological Information in the Intrinsic Alignments of Luminous Red Galaxies

The intrinsic alignments of galaxies are usually regarded as a contaminant to weak gravitational lensing observables. The alignment of Luminous Red Galaxies, detected unambiguously in observations from the Sloan Digital Sky Survey, can be reproduced by the linear tidal alignment model of Catelan, Kamionkowski & Blandford (2001) on large scales. In this work, we explore the cosmological information encoded in the intrinsic alignments of red galaxies. We make forecasts for the ability of current and future spectroscopic surveys to constrain local primordial non-Gaussianity and Baryon Acoustic Oscillations (BAO) in the cross-correlation function of intrinsic alignments and the galaxy density field. For the Baryon Oscillation Spectroscopic Survey, we find that the BAO signal in the intrinsic alignments is marginally significant with a signal-to-noise ratio of 1.8 and 2.2 with the current LOWZ and CMASS samples of galaxies, respectively, and increasing to 2.3 and 2.7 once the survey is completed. For the Dark Energy Spectroscopic Instrument and for a spectroscopic survey following the EUCLID redshift selection function, we find signal-to-noise ratios of 12 and 15, respectively. Local type primordial non-Gaussianity, parametrized by fNL = 10, is only marginally significant in the intrinsic alignments signal with signal-to-noise ratios < 2 for the three surveys considered.Comment: 20 pages, 13 figures, version accepted to JCA