Researchers have developed a new approach to calculating cosmological correlators, crucial for understanding primordial fluctuations in the early universe. The foundation of this method lies in the observation that, deep inside the Hubble radius, cosmological modes oscillate as flat-space plane waves. The curvature of spacetime only makes itself felt as these modes are stretched towards the cosmological horizon. This approach significantly simplifies calculations by transforming complex curved-space integrals into elementary flat-space ones.

The technique employs a Laplace transform to decompose each curved-space mode function into a continuous superposition of plane waves. These waves are labeled by a dual variable and “dressed” by a kernel that encodes the spacetime geometry, field content, and underlying dynamics. This formalism allows for the establishment of simple diagrammatic rules for calculating cosmological correlators, analogous to Feynman diagrams in quantum field theory, but adapted to the cosmological context.

As a demonstration, the method was applied to the massive single-exchange correlator. The Laplace representation transparently reveals total and partial energy singularities “from flat space,” and yields a closed-form series that converges rapidly throughout the entire kinematic domain. Although developed for conformally coupled fields exchanging massive scalars in de Sitter space, the approach is adaptable to most situations of interest in primordial cosmology, promising a powerful computational tool for future studies of the early universe.