Abstract: Axions, scalar fields with compact field spaces, are some of the most well-motivated candidates for physics beyond the Standard Model. In this talk, I will explain how inflationary correlations are uniquely sensitive to the topology of a scalar's field space, and can thus be used to distinguish axions from other light scalar fields even if they share the exact same action. I will show that axions can have a qualitatively distinct impact on a heavy field's cosmological collider signal, which can be used to directly measure the axion's decay constant.