Disentangling mass spectra of multiple fields in cosmological collider

TL;DR

This paper investigates how multiple scalar fields with similar masses influence the inflationary bispectrum, proposing that specific oscillatory features can help distinguish nearly degenerate mass spectra in cosmological observations.

Contribution

It introduces a method to identify nearly degenerate scalar field masses through characteristic oscillations in the bispectrum, aiding in disentangling complex mass spectra in the early universe.

Findings

Oscillating bispectrum features reveal mass differences.

Longer wavelength waveforms help identify degenerate masses.

Potential for future observations to detect multiple particles.

Abstract

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.