Multifield Inflation after Planck: The Case for Nonminimal Couplings

TL;DR

Multifield inflation models with nonminimal couplings align well with Planck data, predict observable parameters within favored ranges, and can explain low CMB power at low multipoles, with future measurements capable of distinguishing models.

Contribution

This paper demonstrates that multifield inflation models with nonminimal couplings are consistent with Planck observations and can account for specific CMB anomalies, highlighting their observational viability.

Findings

Models evolve along single-field attractors

Predicted spectral index and tensor-to-scalar ratio match observations

Can amplify isocurvature perturbations to explain low CMB power

Abstract

Multifield models of inflation with nonminimal couplings are in excellent agreement with the recent results from {\it Planck}. Across a broad range of couplings and initial conditions, such models evolve along an effectively single-field attractor solution and predict values of the primordial spectral index and its running, the tensor-to-scalar ratio, and non-Gaussianities squarely in the observationally most-favored region. Such models also can amplify isocurvature perturbations, which could account for the low power recently observed in the CMB power spectrum at low multipoles. Future measurements of primordial isocurvature perturbations and the tensor-to-scalar ratio may serve to distinguish between the currently viable possibilities.