Axion Isocurvature Collider

Abstract

Cosmological colliders can preserve information from interactions at very high energy scale, and imprint them on cosmological observables. Taking the squeezed limit of cosmological perturbation bispectrum, information of the intermediate particle can be directly extracted from observations such as cosmological microwave background (CMB). Thus cosmological colliders can be powerful and promising tools to test theoretical models. In this paper, we study extremely light axions (including QCD axions and axion-like-particles), and consider them constituting cold dark matter (CDM) at late times. We are interested in inflationary isocurvature modes by such axions, and try to figure out how axion perturbations can behave as isocurvature colliders. We work out an example where the intermediate particle is a boson, and show that, in the squeezed limit, it is possible to provide a clock signal of significant amplitudes, with a characteristic angular dependence. This provides a channel to contribute and analyze clock signals of isocurvature bispectrum, which we may hopefully see in future experiments.

36 pages, 8 figures

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• Missing Scalars at the Cosmological Collider
• Closed-Form Formulae for Inflation Correlators
• Parity-Odd and Even Trispectrum from Axion Inflation
• Classical Cosmological Collider Physics and Primordial Features
• NANOGrav signal from axion inflation
• Gravitational Wave Probes of Massive Gauge Bosons at the Cosmological Collider
• Continuous Spectrum on Cosmological Collider
• An Effective Cosmological Collider
• Analytic Formulae for Inflationary Correlators with Dynamical Mass
• Fingerprints of a Non-Inflationary Universe from Massive Fields
• A Match Made in Heaven: Linking Observables in Inflationary Cosmology
• Non-Gaussianity from explicit $U(1)$-breaking interactions