Inflation models and observation

TL;DR

This paper catalogs inflationary potentials from the EFT-grounded small-field models to large-field chaotic and multi-field constructions, detailing how current and upcoming observations constrain $n-1$ and $r$ and how these constraints delineate viable regions in the $r$–$n$ plane. It provides explicit predictions for slow-roll parameters, curvature perturbations, tensor modes, running, and non-Gaussianity across model classes, including single- and multi-component scenarios such as $N$-flation, New/Modular, and $F$- and $D$-term inflation, as well as concave-upward and concave-downward potentials. A key contribution is the first prediction of the trispectrum in a generic multi-field model and the systematic discussion of how post-inflationary history affects $N$. The work emphasizes that Planck and future surveys will sharply discriminate among small-field and large-field models, with non-Gaussianity offering a decisive falsification criterion for many slow-roll pictures, and it connects inflationary physics to high-energy theory through EFT and moduli-inspired constructions.

Abstract

We consider small-field models which invoke the usual framework for the effective field theory, and large-field models which go beyond that. Present and future possibilities for discriminating between the models are assessed, on the assumption that the primordial curvature perturbation is generated during inflation. With PLANCK data, the theoretical and observational uncertainties on the spectral index will be comparable, providing useful discrimination between small-field models. Further discrimination between models may come later through the tensor fraction, the running of the spectral index and non-gaussianity. The prediction for the trispectrum in a generic multi-field inflation model is given for the first time.

Figures (12)

• Figure 1: The large-field region corresponding to $\Delta\phi_N >M_{\rm P}$ is shaded in dark grey. The region corresponding instead to $\Delta\phi_N>0.1M_{\rm P}$ is lightly shaded. To be eventually observable $r$ should be above the black horizontal line.
• Figure 2: Figure \ref{['rlog']} is plotted on a linear scale.
• Figure 3: The curved lines are the Natural Inflation predictions for $N=20$ and $N=75$, and the horizontal lines are the corresponding multi-component Chaotic Inflation predictions. The junction of each pair of lines corresponds to single-component Chaotic Inflation. The regions allowed by observation with various assumptions are taken from tegmarketal.
• Figure 4: New inflation, modular inflation, etc.
• Figure 5: $F$- and $D$-term inflation, mutated hybrid, $D$-branes etc.