FOREGROUND CONTROL AND CHARACTERIZATION IN COSMIC MICROWAVE BACKGROUND EXPERIMENTS

The CMB is a relic radiation from the early stage of the Universe, when radiation was initially coupled with the primordial plasma, currently detected as a blackbody spectrum in the microwave range. Measuring its intensity anisotropies and the so-called E-modes polarization pattern have proven to be powerful tools to constrain the cosmological parameters to sub-percent precision. The present and future challenges in CMB observations are represented by two scenarios: polarization measurements to detect a specific pattern, called B-modes, which, according to the Inflation theory, should have been caused by the presence of gravitational waves in the primordial plasma, and tiny spectral distortions to the CMB blackbody emission, predicted both within and beyond the ΛCDM theory. Both signals are faint (below µK) and their detection thus requires instruments with ultra-low noise, excellent control over instrumental systematic effects, and accurate foreground removal, which is the contamination from spurious sky signals, such as the Galactic microwave emission, dominated by the synchrotron and thermal dust contributions, or our atmosphere. My research activity has focused on the foreground control and characterization for two ground-based CMB experiments: QUBIC (Q & U Bolometric Interferometer for Cosmology), which is the first-ever experiment for CMB polarization measurements that combines bolometric detectors with interferometry, instead of relying on traditional direct-imaging methods, and COSMO (COSmic Monopole Observer), a ground-based experiment for CMB spectral distortion measurements. My contribution to QUBIC is divided into three studies: simulations of foreground removal, characterization of the atmospheric contribution at the observing site, in Argentina, and a preliminary performance forecast for the QUBIC-TD, which is a reduced version of the final instrument constructed to demonstrate bolometric interferometry, currently installed in Argentina. For COSMO, instead, I performed laboratory measurements to characterize its multi-mode antenna system, which I designed before my PhD.