The simplest extension of Starobinsky inflation

TL;DR

This paper introduces a minimal extension to the Starobinsky inflation model by adding an extra scalar field, demonstrating compatibility with Planck data and supporting supergravity embedding.

Contribution

It presents the first detailed analysis of a simple scalar extension to Starobinsky inflation, showing it fits observational data without fine-tuning.

Findings

Model predictions align with Planck data

No fine-tuning required for compatibility

Supports embedding in supergravity frameworks

Abstract

We consider the simplest extension to the Starobinsky model, by allowing an extra scalar field to help drive inflation. We perform our analysis in the Einstein frame and calculate the power spectra at the end of inflation to second order in the slow--roll parameters. We find that the model gives predictions in great agreement with the current Planck data without the need for fine-tuning. Our results encourage current efforts to embed the model in a supergravity setting.