Exact bispectra in strongly mixed multifield inflation
Abstract
Using the effective field theory of inflationary fluctuations extended by a massive isocurvature scalar, at unit sound speed, we compute the primordial bispectra generated by every cubic interaction of dimension four or less in the unitary gauge, with the curvature--isocurvature quadratic mixing resummed to all orders in the dimensionless mixing strength λ=ρ/H. Placing the mixing in the free Hamiltonian [...], every scale-invariant tree-level bispectrum reduces to a single Schwinger-parameter integral over independent leg kernels, and what perturbation theory calls single, double and triple exchange are contact diagrams of the resummed theory. At strong mixing we unveil genuinely new, exact multifield bispectrum shapes with no correlation to the standard shapes used in data analyses. The squeezed limit carries a cosmological collider signal with a universal frequency set by the dressed mass parameter μeff at every exchange order. At weak mixing the clock coefficients are obtained in closed form and reduce [...] to the known perturbative single- and double-exchange results, exactly; the triple-exchange leading coefficient is obtained in closed form at every mass, in terms of hypergeometric functions, for the first time. At strong mixing the collider amplitude scales as eπ(λ−2μeff)/2 over the whole (λ,μeff) plane. This encompasses all previously studied regimes as particular cases [...]. A first confrontation of the six exact shapes with the Planck PR4 binned bispectrum shows a preference for strong mixing, where the cosmological collider oscillations invade mildly squeezed configurations [...]. The shapes of all interactions over the whole plane [...] are released with the code that produced them, so that a template at any mixing and mass can be read off in milliseconds.
Related
- Pushing the Primordial Frontier: Exact Linear Solutions in Multifield Inflation
- Explicit gauge-invariant variables in multifield inflation beyond linear order and Hamiltonian dynamics
- Strongly mixed cosmological collider at unequal sound speeds
- Carving out the Multifield Cosmological Collider Landscape
- New Effects in Multifield Cosmology Coupled to the Gauss-Bonnet Term
BibTeX
@misc{pinol2026exact,
title = {{Exact bispectra in strongly mixed multifield inflation}},
author = {Lucas Pinol},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.38167},
eprint = {2609.38167},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05781908v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Exact bispectra in strongly mixed multifield inflation
AU - Lucas Pinol
PY - 2026
DA - 2026/09/29
PB - HAL
DO - 10.48550/arxiv.2609.38167
UR - https://hal.science/hal-05781908v1
AB - Using the effective field theory of inflationary fluctuations extended by a massive isocurvature scalar, at unit sound speed, we compute the primordial bispectra generated by every cubic interaction of dimension four or less in the unitary gauge, with the curvature--isocurvature quadratic mixing resummed to all orders in the dimensionless mixing strength λ=ρ/H. Placing the mixing in the free Hamiltonian [...], every scale-invariant tree-level bispectrum reduces to a single Schwinger-parameter integral over independent leg kernels, and what perturbation theory calls single, double and triple exchange are contact diagrams of the resummed theory. At strong mixing we unveil genuinely new, exact multifield bispectrum shapes with no correlation to the standard shapes used in data analyses. The squeezed limit carries a cosmological collider signal with a universal frequency set by the dressed mass parameter μ_eff at every exchange order. At weak mixing the clock coefficients are obtained in closed form and reduce [...] to the known perturbative single- and double-exchange results, exactly; the triple-exchange leading coefficient is obtained in closed form at every mass, in terms of hypergeometric functions, for the first time. At strong mixing the collider amplitude scales as e^π(λ−2μ_eff)/2 over the whole (λ,μ_eff) plane. This encompasses all previously studied regimes as particular cases [...]. A first confrontation of the six exact shapes with the Planck PR4 binned bispectrum shows a preference for strong mixing, where the cosmological collider oscillations invade mildly squeezed configurations [...]. The shapes of all interactions over the whole plane [...] are released with the code that produced them, so that a template at any mixing and mass can be read off in milliseconds.
ER -