Natural Inflation on the brane with a TeV-scale gravity: Parameter constraints after Planck 2015

TL;DR

This paper investigates Natural Inflation within the Randall-Sundrum II brane model, analyzing parameter constraints based on Planck 2015 data, and explores the implications of a TeV-scale 5D Planck mass for inflationary dynamics.

Contribution

It provides a detailed analysis of Natural Inflation on the brane with a TeV-scale gravity, deriving parameter constraints and demonstrating model viability with current observational data.

Findings

Model is compatible with Planck 2015 results.

For a 5D Planck mass around 10 TeV, all parameters are determined.

Sub-Planckian inflaton field excursions are achieved.

Abstract

In the present work we have studied Natural Inflation in the framework of the Randall-Sundrum II brane model (RS-II) in the light of the latest Planck results. Adopting the Randall-Sundrum fine-tuning, the model is characterized by 3 parameters in total, namely the 5-dimensional Planck mass $M_5$ and the two mass scales of the inflaton potential $f$ and $\Lambda$. We show in the $n_s-r$ plane the theoretical predictions of the model together with the allowed contour plots, and we conclude that the model is viable. By using the Planck results only it is possible to determine the two mass scales of the inflaton potential in terms of $M_5$, which remains undetermined. However, there are several good theoretical reasons to consider a higher-dimensional Planck mass of the order of $10 TeV$, which is compatible with primordial nucleosynthesis. If we insist on considering a $M_5$ of this order of magnitude all parameters are known and a sub-Planckian excursion of the inflaton scalar field is achieved.