Disentangling mass spectra of multiple fields in cosmological collider
  We study effects of multiple scalar fields (scalar isocurvatons) with the
Hubble scale masses on the inflationary bispectrum in the squeezed limit,
particular paying attention to the question how to disentangle mass spectra of
such fields. We consider two isocurvatons with almost degenerate masses and the
coupling of an inflaton to both isocurvatons as an example. We find that the
characteristic feature associated with nearly degenerate masses appears in the
oscillating part of the bispectrum, which is dominated by a waveform with a
specific wavelength roughly given by an inverse of the mass difference. Such a
waveform with a relatively longer wavelength can be easily identified and
useful for disentangling almost degenerate mass spectra. This situation is in
sharp contrast with the case of collider experiments on earth, where the very
precise energy resolution corresponding to the mass difference is required to
disentangle almost degenerate mass spectra. Therefore, if future observations
could detect this kind of a characteristic feature in bispectrum of the
primordial curvature perturbations, it can prove the existence of degenerate
multiple particles around the Hubble scale and resolve their mass degeneracies.
