Inflation with very small tensor-to-scalar ratio

TL;DR

This paper examines inflation models predicting very small tensor-to-scalar ratios, comparing their predictions with Planck 2018 data and discussing future observational prospects related to quantum fluctuations.

Contribution

It provides a detailed comparison of inflation models with very small r against current cosmological data and explores implications for future measurements.

Findings

Models with very small r are consistent with Planck 2018 data.

Future tensor-to-scalar ratio measurements can test these inflation models.

Quantum fluctuation origins are relevant for understanding small r predictions.

Abstract

We have investigated inflation models that predict a very small value of the tensor-to-scalar ratio, $r$. The spectral index $n_s$, and the tensor-to-scalar ratio $r$, are strictly constrained by the Planck data. $n_s$ and $r$ are sensitive to the shape and magnitude of the inflaton potential, respectively.The constraints by the Planck 2018 data combined with other cosmological observations are compared with the predictions from the inflation models regarding $n_s$ and $r$. Furthermore, we discuss the comparison of future tensor-to-scalar ratio data with predictions from the inflation models with a focus on part of the quantum fluctuation origin.