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Primordial Features as Evidence for Inflation

In the primordial universe, fields with mass much larger than the mass-scale of the event-horizon (such as the Hubble parameter in inflation) exist ubiquitously, and can be excited from time to time and oscillate quickly around their minima. These excitations can induce specific patterns in density perturbations, which record the time dependence of the scale factor of the primordial universe, thus provide direct evidence for the inflation paradigm or its alternatives. Such effects are conventionally averaged out in theoretical and data analyses, but can be accessible for experiments targeting on density perturbations with high multipoles.