Abstract
Background Imaging of Cosmic Extragalactic Polarization (BICEP) is a bolometric polarimeter designed to measure the inflationary B-mode polarization of the cosmic microwave background (CMB) at degree angular scales. During three seasons of observing at the South Pole (2006 through 2008), BICEP mapped ~2% of the sky chosen to be uniquely clean of polarized foreground emission. Here we present initial results derived from a subset of the data acquired during the first two years. We present maps of temperature, Stokes Q and U, E and B modes, and associated angular power spectra. We demonstrate that the polarization data are self-consistent by performing a series of jackknife tests. We study potential systematic errors in detail and show that they are sub-dominant to the statistical errors. We measure the E-mode angular power spectrum with high precision at 21 < ell < 335, detecting for the first time the peak expected at ell ~ 140. The measured E-mode spectrum is consistent with expectations from a LCDM model, and the B-mode spectrum is consistent with zero. The tensor-to-scalar ratio derived from the B-mode spectrum is r = 0.03+0.31-0.26, or r < 0.72 at 95% confidence, the first meaningful constraint on the inflationary gravitational wave background to come directly from CMB B-mode polarization.
Highlights
One of the cornerstones in our current understanding of cosmology is the theory of inflation
The Wilkinson Microwave Anisotropy Probe (WMAP) MCMC map has poor signal-to-noise ratio (S/N) in regions far from the Galactic plane, and we have found that within the Background Imaging of Cosmic Extragalactic Polarization (Bicep) cosmic microwave background (CMB) field, the map is dominated by variance in the Monte Carlo fit
Motivated by the exciting possibility of detecting, albeit indirectly, the gravitational wave background due to inflation, many efforts are underway to develop the instrumentation and methods necessary to search for the B-mode component of CMB polarization at degree angular scales
Summary
One of the cornerstones in our current understanding of cosmology is the theory of inflation. Precision measurements of the temperature anisotropies span a wide range of angular scales (Jones et al 2006; Reichardt et al 2009; Nolta et al 2009; Friedman et al 2009; Sievers et al 2009; Brown et al 2009) and have yielded tight constraints on a model of the universe in which the energy content is dominated by a cosmological constant and cold dark matter (ΛCDM). Because density fluctuations at the surface of last scattering create only E-mode polarization, a detection of the B-mode signal would be strong evidence that inflation occurred (see, e.g., Dodelson et al 2009). The inflationary B-mode amplitude is parameterized by the tensor-to-scalar ratio r, and the most restrictive published upper limit, r < 0.22 (95% confidence), comes from measurements of large-scale temperature anisotropies in combination with baryon acoustic oscillation and Type Ia supernova data (Komatsu et al 2009).
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