Master thesis defense by Alexandra Zisimopoulou

The CMB on Large Angular Scales

 This thesis is dedicated to the description of the anomalies in the Cosmic Microwave Background (CMB) that have been observed on large angular scales and to the description of a theoretical framework that can possibly explain the nature of the dipolar power asymmetry observed in the CMB. Planck Collaboration of 2018, confirmed several anomalies in the emperature map of the CMB on large angular scales, namely, the power asymmetry, the Cold Spot and other temperature peaks, the lack of large angle correlations and the pointparity asymmetry. Planck¿s mission searched for equivalent asymmetries in the polarization maps but the anomalies were not detected at a significant statistical level. Low signal-to-noise of the Planck¿s polarization data is a limiting factor and future, more sensitive observations are required to better investigate these
anomalies. It is however intriguing to understand the origin of the anomalies in the temperature maps. It is suggested that the dipolar power asymmetry can be explained by the existence of an intrinsic CMB dipole. This temperature dipole is originated from superhorizon sized primordial isocurvature perturbations that existed in the axion field during inflation.