On the inflationary massive field with a curved field manifold

TL;DR

This paper explores how curved field space geometry during inflation affects massive fields and their observable signatures, revealing that curvature induces significant mass corrections and modifies non-Gaussianity scaling, offering new ways to probe fundamental physics.

Contribution

It extends quasi-single field inflation models to curved field manifolds, deriving how curvature influences mass corrections and non-Gaussianity, linking geometry to observable signatures.

Findings

Curvature induces order-Hubble scale mass corrections.

Mass correction's time dependence affects bispectrum scaling.

Field space curvature can be probed via non-Gaussianity signatures.

Abstract

Massive fields during inflation provide an interesting opportunity to test new physics at very high energy scales. Meanwhile in fundamental realizations, the inflationary field space typically has a curved geometry, which may leave detectable imprints in primordial observables. In this paper we study an extension of quasi-single field inflation where the inflaton and the massive field belong to a curved field manifold. Because of the nontrivial field space curvature, the massive field here can get significant mass corrections of order the Hubble scale, thus the quasi-single field predictions on primordial non-Gaussianity are affected. We derive the same result in an equivalent approach by using the background effective field theory of inflation, where a dimension-6 operator is identified to play an important role and its cutoff scale is associated with the curvature scale of the field space. In addition, due to the slow-roll evolution of the inflaton, this type of mass correction has intrinsic time-dependence. Consequently, the running mass modifies the scaling behaviour in the squeezed limit of the scalar bispectrum, while the resulting running index measures the curvature of the internal field space. Therefore the minimal setup of a massive field within curved field space during inflation may naturally lead to new observational signatures of the field space geometry.