2,072 research outputs found
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
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