Laplace space for cosmological correlators

Abstract
Deep inside the horizon, every cosmological mode oscillates as a flat-space plane wave. A Laplace transform turns this fact into a general method: it resolves each curved-space mode into a superposition of plane waves dressed by a kernel that encodes the spacetime geometry, field content and dynamics. This provides simple diagrammatic rules that turn cosmological correlator diagrams into their flat-space counterparts integrated against Laplace-space kernels. This integral representation makes the energy singularities of correlators manifest and, on the paradigmatic massive single exchange, it evaluates as a single series valid throughout the kinematic domain. The Laplace representation also solves the linear dynamics of a massive field linearly coupled to the curvature perturbation, which has long resisted analytical treatment, at any mixing strength. The bispectrum follows as a rapidly convergent series of elementary functions, capturing all exchange orders at once. We find that the cosmological collider signal at strong mixing is larger than widely believed and can dominate the bispectrum.

You can also attend online on Teams: High Energy Theory Seminar | Meeting-Join | Microsoft Teams