Inflationary paradigm in trouble after Planck2013

TL;DR

Recent Planck data challenges the viability of many inflationary models, especially simple and plateau-like ones, raising fundamental issues and calling for new approaches in cosmology.

Contribution

The paper critically assesses the impact of Planck2013 results on inflationary models, highlighting new theoretical problems and the need for alternative explanations.

Findings

Simplest inflation models are statistically disfavored by data.

Plateau-like models face three major theoretical problems.

Upcoming experiments could provide decisive tests.

Abstract

Recent results from the Planck satellite combined with earlier observations from WMAP, ACT, SPT and other experiments eliminate a wide spectrum of more complex inflationary models and favor models with a single scalar field, as reported by the Planck Collaboration. More important, though, is that all the simplest inflaton models are disfavored statistically relative to those with plateau-like potentials. We discuss how a restriction to plateau-like models has three independent serious drawbacks: it exacerbates both the initial conditions problem and the multiverse-unpredictability problem and it creates a new difficulty that we call the inflationary "unlikeliness problem." Finally, we comment on problems reconciling inflation with a standard model Higgs, as suggested by recent LHC results. In sum, we find that recent experimental data disfavors all the best-motivated inflationary scenarios and introduces new, serious difficulties that cut to the core of the inflationary paradigm. Forthcoming searches for B-modes, non-Gaussianity and new particles should be decisive.