My major research interests have been the effects from particle interactions during inflation. Couplings between different fields can lead to particle production, and the produced quanta can in turn interact with cosmological perturbations, leaving visible imprints on the non-Gaussianity and gravitational-wave (GW) signals. In some cases, GW signals from this mechanism can be large enough to be detectable even at the terrestrial GW detectors. I also studied models of vector fields that break the rotational invariance of space, which can result in broken statistical isotropy in the cosmic microwave background and large-scale structure.