Strongly mixed cosmological collider at unequal sound speeds
Abstract
We derive the canonically normalized modes of a two-field inflationary system with arbitrary constant quadratic mixing and unequal sound speeds cφ and cσ for the curvature and isocurvature perturbations, respectively. A Laplace representation reduces the coupled dynamics to a second-order Heun equation and gives the exact late-time curvature power spectrum for arbitrary values of the mixing parameter and entropy mass. The sound-speed ratio rc=cσ/cφ controls the separation between the two sound horizons. At fixed nonzero mixing and rc≪1, the power exhibits power-law enhancement, growth as ln2(1/rc), or bounded oscillations in ln rc, depending on the mass and mixing. For rc≫1, the correction to the unmixed spectrum vanishes as ln rc/rc2 at fixed mass and mixing. Using the same normalized modes, we compute the tree-level bispectrum for three representative cubic interactions, with the mixing parameter treated exactly. For heavy entropy fields, unequal speeds modify the collider amplitude and phase while preserving the strict squeezed frequency set by the final entropy mass. The power-normalized amplitude can vary nonmonotonically with rc, and a sound-speed hierarchy can delay the approach to this asymptotic regime.
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BibTeX
@misc{huenupi2026strongly,
title = {{Strongly mixed cosmological collider at unequal sound speeds}},
author = {Javier Huenupi and Gonzalo A. Palma and Spyros Sypsas},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.02138},
eprint = {2610.02138},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.02138},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Strongly mixed cosmological collider at unequal sound speeds
AU - Javier Huenupi
AU - Gonzalo A. Palma
AU - Spyros Sypsas
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2610.02138
UR - https://arxiv.org/abs/2610.02138
AB - We derive the canonically normalized modes of a two-field inflationary system with arbitrary constant quadratic mixing and unequal sound speeds c_φ and c_σ for the curvature and isocurvature perturbations, respectively. A Laplace representation reduces the coupled dynamics to a second-order Heun equation and gives the exact late-time curvature power spectrum for arbitrary values of the mixing parameter and entropy mass. The sound-speed ratio r_c=c_σ/c_φ controls the separation between the two sound horizons. At fixed nonzero mixing and r_c≪1, the power exhibits power-law enhancement, growth as ln^2(1/r_c), or bounded oscillations in ln r_c, depending on the mass and mixing. For r_c≫1, the correction to the unmixed spectrum vanishes as ln r_c/r_c^2 at fixed mass and mixing. Using the same normalized modes, we compute the tree-level bispectrum for three representative cubic interactions, with the mixing parameter treated exactly. For heavy entropy fields, unequal speeds modify the collider amplitude and phase while preserving the strict squeezed frequency set by the final entropy mass. The power-normalized amplitude can vary nonmonotonically with r_c, and a sound-speed hierarchy can delay the approach to this asymptotic regime.
ER -