Detection of polarization in the cosmic microwave background using DASI

The past several years have seen the emergence of a new standard cosmological model in which small temperature differences in the cosmic microwave background (CMB) on degree angular scales are understood to arise from acoustic oscillations in the hot plasma of the early universe sourced by primordial adiabatic density fluctuations. In the context of this model, recent measurements of the temperature fluctuations have led to profound conclusions about the origin, evolution and composition of the universe. Given knowledge of the temperature angular power spectrum, this theoretical framework yields a prediction for the level of the CMB polarization with essentially no free parameters. A determination of the CMB polarization would therefore provide a critical test of the underlying theoretical framework of this standard model.; In this thesis, we report the detection of polarized anisotropy in the Cosmic Microwave Background radiation with the Degree Angular Scale Interferometer (DASI), located at the Amundsen-Scott South Pole research station. Observations in all four Stokes parameters were obtained within two 3°4 FWHM fields separated by one hour in Right Ascension. The fields were selected from the subset of fields observed with DASI in 2000 in which no point sources were detected and are located in regions of low Galactic synchrotron and dust emission. The temperature angular power spectrum is consistent with previous measurements and its measured frequency spectral index is −0.01 (−0.16 to 0.14 at 68% confidence), where zero corresponds to a 2.73 K Planck spectrum. The power spectrum of the detected polarization is consistent with theoretical predictions based on the interpretation of CMB anisotropy as arising from primordial scalar adiabatic fluctuations. Specifically, E-mode polarization is detected at high confidence (4.9σ). Assuming a shape for the power spectrum consistent with previous temperature measurements, the level found for the E-mode polarization is 0.80 (0.56 to 1.10), where the predicted level given previous temperature data is 0.9 to 1.1. At 95% confidence, an upper limit of 0.59 is set to the level of B-mode polarization with the same shape and normalization as the E-mode spectrum. The TE correlation of the temperature and E-mode polarization is detected at 95% confidence, and also found to be consistent with predictions. These results provide strong validation of the standard model framework for the origin of CMB anisotropy and lend confidence to the values of the cosmological parameters that have been derived from CMB measurements.