Parity violation in the Cosmic Microwave Background from a pseudoscalar inflaton

If the inflaton phi is a pseudoscalar, then it naturally interacts with gauge fields through the coupling proportional to phi F-mu nu (F) over tilde (mu nu). 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.