Description
Abstract: We show that, while inflation can be regarded as a cosmological collider with fixed energy, possible alternative scenarios to inflation may be viewed as particle detectors with scanning energies. They scan through a tower of massive particles in the primordial universe and leave a series of bursts of oscillatory signals as scale-dependent features in the density perturbations. Besides particle contents, these signals directly record the time evolution of the scale factor of the primordial universe. We discuss observational aspects of these signals.
