# Rescuing Quartic and Natural Inflation in the Palatini Formalism

## TL;DR

This paper demonstrates that minimally coupled quartic and natural inflation models, previously excluded by observational data, can be made viable within the Palatini formalism by adding an $R^2$ term.

## Contribution

It shows how adding an $R^2$ term in the Palatini formalism rescues certain inflation models from observational exclusion.

## Key findings

- Quartic and natural inflation models become compatible with Planck data.
- Adding $R^2$ term in Palatini formalism alters inflationary predictions.
- Rescued models fit current cosmological observations.

## Abstract

When considered in the Palatini formalism, the Starobinsky model does not provide us with a mechanism for inflation due to the absence of a propagating scalar degree of freedom. By (non)--minimally coupling scalar fields to the Starobinsky model in the Palatini formalism we can in principle describe the inflationary epoch. In this article, we focus on the minimally coupled quartic and natural inflation models. Both theories are excluded in their simplest realization since they predict values for the inflationary observables that are outside the limits set by the Planck data. However, with the addition of the $R^2$ term and the use of the Palatini formalism, we show that these models can be rendered viable.