A Match Made in Heaven: Linking Observables in Inflationary Cosmology

Stefanyszyn, David; Tong, Xi; Zhu, Yuhang

Abstract

Cosmological correlation functions of inflaton and graviton perturbations are the fundamental observables of early universe cosmology and remain a primary target for observations. In this work, we ask the following question: are these observables independent of one another? We find that in the parity-odd sector of inflationary perturbation theory, the answer is a resounding no! In earlier work we derived a correlator-to-correlator factorisation formula which states that parity-odd correlators factorise into lower-point correlators under some mild assumptions on the underlying theory. In this work, we show that these assumptions are satisfied in dynamical Chern-Simons gravity where the action of minimal inflation is augmented by a coupling between the inflaton and the gravitational Chern-Simons term. Such a theory gives rise to a parity-odd trispectrum of curvature perturbations, and we show that such a trispectrum can be expressed solely in terms of the bispectrum that arises due to the minimal coupling between the inflaton and graviton, and the graviton power spectrum which receives a parity-odd correction in this theory. The trispectrum is quadratic in this mixed inflaton-graviton bispectrum and can therefore be interpreted as a ``double copy". Our final expression for the parity-odd trispectrum is a relatively simple function of the external momenta that is rational and factorised.

Citation

Stefanyszyn, D., Tong, X., & Zhu, Y. (2025). A Match Made in Heaven: Linking Observables in Inflationary Cosmology

• Working Paper Type: Preprint
• Online Publication Date: May 21, 2025
• Publication Date: May 21, 2025
• Deposit Date: Aug 1, 2025
• Publicly Available Date: Aug 4, 2025
• DOI: https://doi.org/10.48550/arXiv.2505.16071
• Public URL: https://nottingham-repository.worktribe.com/output/52225246
• Publisher URL: https://arxiv.org/abs/2505.16071