Gauge field production in supergravity inflation: Local non-Gaussianity and primordial black holes

When inflation is driven by a pseudoscalar field coupled to vectors as 4F, this coupling may lead to a copious production of gauge quanta, which in turns induces non-Gaussian and non-scale-invariant corrections to curvature perturbations. We point out that this mechanism is generically at work in a broad class of inflationary models in supergravity, hence providing them with a rich set of observational predictions. When the gauge fields are massless, significant effects on cosmic microwave background scales emerge only for relatively large. We show that in this regime, the curvature perturbations produced at the last stages of inflation have a relatively large amplitude that is of the order of the upper bound set by the possible production of primordial black holes by non-Gaussian perturbations. On the other hand, within the supergravity framework described in our paper, the gauge fields can often acquire a mass through a coupling to additional light scalar fields. Perturbations of these fields modulate the duration of inflation, which serves as a source for non-Gaussian perturbations of the metric. In this regime, the bounds from primordial black holes are parametrically satisfied and non-Gaussianity of the local type can be generated at the observationally interesting level f₍₋ (10).