A CMB B-mode Search with Three Years of BICEP Observations

Abstract

Abstract. The search for B-mode, or curl-type, polarization in the Cosmic Microwave Background is the most promising technique to constrain or detect primordial gravitational waves predicted by the theory of inflation. The Bicep telescope, which observed from the South Pole for three years from 2006 through 2008, is the first experiment specifically designed to target this signal. We review the observational motivations for inflation, the advantages of B-mode observations as a technique for detecting the gravitational wave background, and the design features of Bicep that optimize it for this search. The final analysis of all three seasons of Bicep data is in progress, representing a 50% increase in integration time compared to the result from Chiang et al. (2010). A preview of the three year result includes E-mode and B-mode maps, as well as the projected constraint on r, the tensor-to-scalar ratio.Keywords. cosmology: observations, cosmic microwave background, polarization, instrumentation: polarimeters The Cosmic Microwave Background and InflationThe Cosmic Microwave Background (CMB) serves as a unique and invaluable window to our early universe. First discovered by Penzias and Wilson in 1964, the CMB is a relic thermal radiation that was originally emitted during the period of recombination, about 300,000 years after the Big Bang, when the universe had cooled enough that protons and electrons could form neutral Hydrogen. Recombination occurred at a temperature of ∼3,000 K; since then, the size of the universe has increased by a factor of 1,100, so the CMB is observed to have a temperature of 3 K today.The temperature of the CMB is very nearly uniform across the entire sky, with small anisotropies at the 10 −5 level. This uniformity poses a theoretical problem, because the causal horizon at the time of recombination corresponds to an angular scale of only three degrees. The question of how different regions of the universe that are causally disconnected achieved such similar temperatures is known as the horizon problem.A solution to the horizon problem is offered by the theory of inflation. The theory proposes that the universe underwent a period of accelerated expansion for a tiny fraction of a second after the Big Bang (Guth, 1981). The expansion increased the scale factor of the space-time metric by 60 e-foldings, or 10 26 , transforming sub-atomic scales to astronomical ones. The observed temperature uniformity of the universe is explained because the regions that were causally disconnected at recombination were in close, causal proximity before inflation.In addition to the horizon problem, there are several other observed features of our universe that are neatly explained by the theory of inflation.• Observations of the CMB have demonstrated that the spatial geometry of the universe is flat on cosmological scales (de Bernardis et al., 2000). Inflation naturally explains 61 at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921312016687 Downloaded from https://www.cambridge.org/core. IP...