Signature of heavy physics in stochastic gravitational-wave background*

Sudden onset of classical oscillations of a heavy field (mass greater than the inflationary Hubble scale) leaves a characteristic scale-invariance-breaking oscillatory feature in the power spectrum of primordial fluctuations. The presence of these features provides a unique opportunity to detect the dynamics of heavy fields during inflation. While such features are constrained to be small in curvature perturbations, we show that it may not be the case for isocurvature perturbations. I will demonstrate the possibility of observing large primordial features in the stochastic gravitational-wave (GW) background originating from a first-order phase transition in a hidden sector. I will show that the signal can be observably large in the GW map while being completely hidden in the standard curvature perturbations such as those of the Cosmic Microwave Background.