A minimal model of inflation and dark radiation
  We show that a minimal extension of the Standard Model including a new
complex scalar field can explain inflation and the observed effective number of
neutrinos. The real part of the singlet plays the role of the inflaton field,
while the Goldstone boson emerging from the spontaneous symmetry breaking of a
global $U(1)$ symmetry contributes to dark radiation and increases the
effective number of neutrino species by $0.3$ over the Standard Model value.
After detailing the phenomenology of the model, we find that the predicted
inflationary observables are in agreement with the current bounds, once the
dark radiation component is allowed, both within the metric and Palatini
formulation of non-minimally coupled gravity.
