Inflation model selection revisited

TL;DR

This paper updates constraints on primordial perturbations using recent cosmological data, favoring concave inflation potentials and disfavoring monomial models, with implications for inflation theory.

Contribution

It provides new bounds on inflation models based on the latest observational data, especially constraining the tensor-to-scalar ratio and model viability.

Findings

Concave potential inflation models are favored at over 95% CL.

Monomial potential models are disfavored at over 95% CL.

Starobinsky and brane inflation models remain consistent with data.

Abstract

We update the constraints on the power spectra of primordial curvature perturbation and tensor perturbation including Planck data 2015 (P15) and recently released BICEP2/Keck data (BK15), Baryon Acoustic Oscillation data and the Type Ia supernovae data. We find that the upper limits of tensor-to-scalar ratio are $0.061$, $0.064$ and $0.072$ at $95\%$ confidence level (CL) in the $\Lambda$CDM+$r$, $\Lambda$CDM+$r$+$\alpha_s$ and $\Lambda$CDM+$r$+$\alpha_s$+$\beta_s$ models respectively, where $\alpha_s$ and $\beta_s$ are the running of scalar spectral index and running of running. The inflation model with a concave potential is favored at more than $95\%$ CL. In addition, parametrizing the slow-roll parameter $\epsilon\sim 1/N^p$, where $N$ is the e-folding number before the end of inflation and taken in the range of $[50,60]$ and $[14,75]$ respectively, we conclude that the inflation model with a monomial potential $V(\phi)\sim \phi^n$ is disfavored at more than $95\%$ CL, and both the Starobinsky inflation model and brane inflation model are still consistent with the data.