Abstract
In this paper, we present a parameter estimation analysis of the polarization and temperature power spectra from the second and third season of observations with the QUaD experiment. QUaD has for the first time detected multiple acoustic peaks in the E-mode polarization spectrum with high significance. Although QUaD-only parameter constraints are not competitive with previous results for the standard six-parameter ΛCDM cosmology, they do allow meaningful polarization-only parameter analyses for the first time. In a standard six-parameter ΛCDM analysis, we find the QUaD TT power spectrum to be in good agreement with previous results. However, the QUaD polarization data show some tension with ΛCDM. The origin of this 1σ-2σ tension remains unclear, and may point to new physics, residual systematics, or simple random chance. We also combine QUaD with the five-year WMAP data set and the SDSS luminous red galaxies 4th data release power spectrum, and extend our analysis to constrain individual isocurvature mode fractions, constraining cold dark matter density, αcdmi < 0.11 (95% confidence limit (CL)), neutrino density, αndi < 0.26 (95% CL), and neutrino velocity, αnvi < 0.23 (95% CL), modes. Our analysis sets a benchmark for future polarization experiments.
Highlights
The anisotropies of the cosmic microwave background (CMB) radiation are among the most important tests of cosmology
A generic prediction of cosmology is that the CMB photons should be polarized at the 10% level
The Monte Carlo Markov Chain (MCMC) method is a method designed to efficiently explore an unknown probability distribution function (PDF) by sequentially drawing samples from it according to a proposal probability function, in our case the Metropolis algorithm (Metropolis et al 1953 among others)
Summary
The anisotropies of the cosmic microwave background (CMB) radiation are among the most important tests of cosmology. The full repository of CMB data available, in conjunction with other cosmological observables, such as data coming from the largescale distribution of galaxies or supernova type Ia observations, are extremely well described by the spatially flat ΛCDM cosmological model. A generic prediction of cosmology is that the CMB photons should be polarized at the 10% level. Current address: Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 OHE, UK. Current address: NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, Maryland 20771, USA. Current address: Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK. Current address: Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
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