Year: 2026
Type: article
Abstract: Heavy-field decoupling removes massive propagating fluctuations from inflationary observables, yet a field-dependent heavy minimum can still define the kinetic geometry seen by surviving light fields. We construct a three-field sigma model in a regime with one adiabatically decoupled transverse scalar and two dynamical light directions. The heavy minimum forms a bounded zero-energy trough, and pullback onto the associated constraint surface produces a curved two-field metric without a localized feature in the classical inflaton potential. At the stationary trough center, the Gauss decomposition assigns the negative light-field curvature to the second fundamental form of the embedded surface. Inflationary motion then changes the connection contribution to the entropy Hessian across the center, placing the strongest entropy instability after the curvature minimum. Complete three-field perturbations converge to the two-light-field calculation as the transverse hierarchy increases, while the induced entropy transfer changes the scalar tilt and running with a much smaller tensor response. A heavy propagator can decouple while the geometry of its minimum remains observable through the light-field spectrum.
Source: Physics Letters B
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W7221152362