Effective field theory of weakly coupled inflationary models

TL;DR

This work extends the single-field EFT of inflation to include scale-dependent interactions induced by heavy fields, yielding a new low-energy regime where the Goldstone boson exhibits a quadratic dispersion relation. The extended EFT remains weakly coupled up to the UV cutoff and predicts observables that depend on the UV-physics scale $\\Lambda_{ m UV} = M c_s^{-1}$ rather than solely on the sound speed, altering the interpretation of the power spectrum, tensor-to-scalar ratio, and non-Gaussianity. By integrating out a heavy field, the authors derive explicit M_n^4 coefficients and show how the dispersion and interaction structure change across energy regimes, including a Schrödinger-like low-energy mode and a lifted strong-coupling scale. The results suggest new phenomenology for inflation and emphasize that UV effects can be captured within a generalized EFT framework without invoking additional light degrees of freedom, with potential observational implications for future CMB and large-scale structure probes.

Abstract

The application of Effective Field Theory (EFT) methods to inflation has taken a central role in our current understanding of the very early universe. The EFT perspective has been particularly useful in analyzing the self-interactions determining the evolution of co-moving curvature perturbations (Goldstone boson modes) and their influence on low-energy observables. However, the standard EFT formalism, to lowest order in spacetime differential operators, does not provide the most general parametrization of a theory that remains weakly coupled throughout the entire low-energy regime. Here we study the EFT formulation by including spacetime differential operators implying a scale dependence of the Goldstone boson self-interactions and its dispersion relation. These operators are shown to arise naturally from the low-energy interaction of the Goldstone boson with heavy fields that have been integrated out. We find that the EFT then stays weakly coupled all the way up to the cutoff scale at which ultraviolet degrees of freedom become operative. This opens up a regime of new physics where the dispersion relation is dominated by a quadratic dependence on the momentum ω~ p^2. In addition, provided that modes crossed the horizon within this energy range, the prediction of inflationary observables - including non-Gaussian signatures - are significantly affected by the new scales characterizing it.