Pushing the Primordial Frontier: Exact Linear Solutions in Multifield Inflation

arXiv:2606.18248 · astro-ph.CO, hep-ph, hep-th · Submitted 2026-06-16 · Read on arXiv

Javier Huenupi, Claudio Muñoz, Gonzalo A. Palma, Spyros Sypsas

astro-ph.CO, hep-ph, hep-th

Submitted: 2026-06-16

Comments: 5 pages + references, 2 figures. v2: Introduced new notation for the canonically normalized curvature perturbation and the Bogoliubov coefficients, and a new definition of the f_M solution

License: http://creativecommons.org/licenses/by/4.0/

The gist: We present exact analytic solutions for the linear dynamics of a two-field inflationary system in which the primordial curvature perturbation zeta is coupled to an isocurvature perturbation sigma of

Terminology

Abstract

We present exact analytic solutions for the linear dynamics of a two-field inflationary system in which the primordial curvature perturbation zeta is coupled to an isocurvature perturbation sigma of entropy mass mu. The solutions are valid for arbitrary values of mu and the dimensionless interaction strength lambda, within a quasi-de Sitter background. They therefore provide analytic control over the strong mixing regime in which zeta interacts with light isocurvature fields, commonly associated with rapid-turn inflation. As a first application, we derive the amplitude of the primordial power spectrum in closed form, obtaining an expression that interpolates between the weakly mixed, strongly mixed, light-field, and heavy-field regimes. These results open the way to analytic studies of multifield observables beyond the power spectrum, including non-Gaussianity, particle production, and loop corrections.

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