Browsing by Author "Troxel, M. A."
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Item Cross-Correlation between Cosmic Microwave Background Lensing and Galaxy Intrinsic Alignment as a Contaminant to Gravitational Lensing Cross-Correlated Probes of the Universe(American Physical Society, 2014-03-25) Troxel, M. A.; Ishak-Boushaki, Mustapha; 0000 0001 2874 3832 (Ishak-Boushaki, M); Troxel, M. A.; Ishak-Boushaki, MustaphaWe introduce here a cross-correlation term between CMB lensing and galaxy intrinsic alignment, noted here as φl. This effect acts as a contaminant to the cross correlation between CMB lensing and galaxy lensing. The latter cross correlation has recently been detected for the first time, and measurements will greatly improve as the area of overlap between galaxy and CMB surveys increases and measurements of the CMB polarization become more significant. This will constitute a powerful probe for studying the structure and evolution of the universe. The magnitude of the φl term is found to be about 15% of the pure CMB lensing- galaxy lensing component and acts to reduce the magnitude of its measured spectrum. This offset in the spectrum will strongly impact its use for precision cosmological study if left unmitigated. We also propose here a method to calibrate this φl contamination through the use of a scaling relation that allows one to reduce the impact of φl by a factor of 20 or more in all redshift bins, which would reduce its magnitude down to detection limits in almost all cases. This will allow the full use of this probe for precision cosmology.Item Stringent Restriction from the Growth of Large-Scale Structure on Apparent Acceleration in Inhomogeneous Cosmological Models(2013-12-19) Ishak-Boushaki, Mustapha; Peel, Austin; Troxel, M. A.; 0000 0001 2874 3832 (Ishak-Boushaki, M); Ishak-Boushaki, Mustapha; Peel, Austin; Troxel, M. A.Probes of cosmic expansion constitute the main basis for arguments to support or refute a possible apparent acceleration due to different expansion rates in the Universe as described by inhomogeneous cosmological models. We present in this Letter a separate argument based on results from an analysis of the growth rate of large-scale structure in the Universe as modeled by the inhomogeneous cosmological models of Szekeres. We use the models with no assumptions of spherical or axial symmetries. We find that while the Szekeres models can fit very well the observed expansion history without a Λ, they fail to produce the observed late-time suppression in the growth unless Λ is added to the dynamics. A simultaneous fit to the supernova and growth factor data shows that the cold dark matter model with a cosmological constant (ΛCDM) provides consistency with the data at a confidence level of 99.65%, while the Szekeres model without Λ achieves only a 60.46% level. When the data sets are considered separately, the Szekeres with no Λ fits the supernova data as well as the ΛCDM does, but provides a very poor fit to the growth data with only 31.31% consistency level compared to 99.99% for the ΛCDM. This absence of late-time growth suppression in inhomogeneous models without a Λ is consolidated by a physical explanation.