The production of cosmic strings and domain walls in the early universe is predicted in a plethora of grand unified theories, but they are expected to survive until the present time potentially leaving behind imprints on the cosmic microwave background (CMB). Although current CMB observations seem to be consistent with the inflationary paradigm, in which the fluctuations are seeded in the very early universe, they also allow for a subdominant topological defect contribution. Domain walls and cosmic strings seed perturbations actively throughout cosmic history and are expected to generate significant vector anisotropies that would not be present in inflation-seeded scenarios. They may, therefore, produce an observationally relevant B-mode polarization signal (despite providing only subdominant contributions to the temperature and E-mode power spectra), which makes this channel a relevant observational window for the detection of topological defects. In this seminar, I will present the cosmic microwave background anisotropies generated by both cosmic string and domain wall networks and describe how these may be obtained through the development of semi-analytical models to describe these networks.
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