# Primordial Perturbations from Multifield Inflation with Nonminimal Couplings - Astrophysics > Cosmology and Nongalactic Astrophysics

Abstract: Realistic models of particle physics include many scalar fields. These fieldsgenerically have nonminimal couplings to the Ricci curvature scalar, either aspart of a generalized Einstein theory or as necessary counterterms forrenormalization in curved background spacetimes. We develop a gauge-invariantformalism for calculating primordial perturbations in models with multiplenonminimally coupled fields. We work in the Jordan frame in which thenonminimal couplings remain explicit and identify two distinct sources ofentropy perturbations for such models. One set of entropy perturbations arisesfrom interactions among the multiple fields. The second set arises from thepresence of nonminimal couplings. Neither of these varieties of entropyperturbations will necessarily be suppressed in the long-wavelength limit, andhence they can amplify the curvature perturbation, $\zeta$, even for modes thathave crossed outside the Hubble radius. Models that overproduce long-wavelengthentropy perturbations endanger the close fit between predicted inflationaryspectra and empirical observations.

Author: David I. Kaiser, Audrey T. Todhunter

Source: https://arxiv.org/