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Parity violation in the Cosmic Microwave Background from a pseudoscalar inflaton

If the inflaton is a pseudoscalar, then it naturally interacts with gauge fields via an axion-like coupling to $F_{μν} \tilde{F}^{μν}$. Through this coupling, the rolling inflaton produces quanta of the gauge field, that in their turn source the tensor components of the metric perturbations. Due to the parity-violating nature of the system, the right- and the left-handed tensor modes have different amplitudes. Such an asymmetry manifests itself in the form of non-vanishing TB and EB correlation functions in the Cosmic Microwave Background (CMB). We compute the amplitude of the parity-violating tensor modes and we discuss two scenarios, consistent with the current data, where parity-violating CMB correlation functions will be detectable in future experiments.