Cosmic Birefringence as a Probe of Fundamental Parity-Violation

The fact that nature exhibits a parity-violating behavior has been mostly accepted since parity is maximally broken in the electroweak sector of the standard model of particle physics. Hence, a question naturally arises: is that possible that besides weak interactions also electromagnetism encode parity-breaking signatures? The purpose of this thesis is to describe how cosmology can provide the natural setting for testing this kind of hypothesis about fundamental physics. In particular, we will show how parity-violating extensions of Maxwell electromagnetism can induce a rotation of the linear polarization plane of photons during propagation, causing the so-called cosmic birefringence. This effect impacts on the cosmic microwave background observations producing a mixing of E and B polarization modes which is otherwise null in the standard scenario. In the literature, several models of cosmic birefringence have been proposed, and most of them involve a Chern-Simons coupling of an axion-like field with the photons, yielding the possibility to exploit such a phenomenon to investigate this kind of exotic cosmic species beyond the standard cosmological paradigm. The structure of this thesis is organized as follows. In Chap. I, we provide all the necessary mathematical tools for understanding the physics of CMB polarization. In Chap. II we discuss the theoretical formalism underlying the theory of cosmological birefringence, and how it is possible ot use it to probe axion-like field as candidates for some components of the Universe's dark sector. In Chap. III, we show how of anisotropic cosmic birefringence is able to induce some promising non-Gaussian signatures and we estimate their signal-to-noise ratio for a future CMB experiment. Chap. IV is dedicated to the conclusion.