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.

Automated summary

The study focuses on the impact of multiple scalar fields with Hubble scale masses on the inflationary bispectrum, specifically examining how to distinguish the mass spectra of these fields. By analyzing two nearly degenerate masses isocurvatons, it is found that the oscillating part of the bispectrum showcases characteristic features that can be useful for disentangling almost degenerate mass spectra. The research suggests that future observations detecting these characteristic features in the bispectrum of primordial curvature perturbations could confirm the existence of degenerate multiple particles at the Hubble scale and resolve their mass degeneracies.