How ghostly particles reshape primordial collider signals

Inflationary collider signals—quantum signatures imprinted in the cosmic microwave background—usually arise from how particles interact. This work shows they can also emerge from how a tilted-ghost spectator particle propagates through spacetime, deforming the wave patterns in a way that produces identical squeezed-limit signatures. The effect is controlled by an effective chemical potential that either boosts or suppresses the signal depending on which oscillatory mode dominates, suggesting cosmological collider phenomenology is more robust and varied than previously realized.