부산대학교 도서관

Summary: Cosmic Inflation is currently the best theory of what took place in the first instant of the Universe. It postulates a brief exponential expansion right after the Big Bang in which the quantum fluctuations are expanded in size to become the initial conditions that seed the growth of structure in the Universe. Most inflationary models predict a stochastic gravitational wave background which would leave a unique B-mode polarization imprint on the Cosmic Microwave Background. The goal of the BICEP/Keck program is to measure the inflationary B-modes, parametrized by the tensor-to-scalar ratio r. A nonzero measurement of r would provide smoking gun evidence for inflation. The BICEP/Keck program have deployed a series of small-aperture, on-axis refracting telescopes, which have been continuously observing at the South Pole since 2006. The tightest constraint on inflationary gravitational waves to date is r< 0.036 using data through the end of 2018.As the statistical power of the measurement increases, so must the effort on systematics control. In this thesis, we review the BICEP/Keck pipeline with an emphasis on both statistical and systematics error mitigation. On reducing statistical uncertainties, we introduce two promising avenues: improved ground subtraction timestream filter and the optimal quadratic estimator on power spectrum. On the systematics mitigation, we present two case studies in which the calibration data are applied to understand the physics behind systematics that are related to the gain calibration. Finally, we introduce the framework of the CMB distortion analysis, which is used as a powerful diagnostics for characterizing the observed B-modes. The distinct signatures in the EB and TB correlations generated by the distortions are used to study the associated physical processes or systematic effects. It is demonstrated that the BK18 data set has no detectable distortion field signatures after the standard systematics mitigations, and we proceed to set competitive constraints on the relevant processes including weak gravitational lensing, cosmic birefringence, and patchy reionization.