Inflation in Extra-Dimensions with one or two branes

TL;DR

This paper explores inflationary models within various extra-dimensional frameworks, analyzing their compatibility with observational data and highlighting the advantages of $oldsymbol{ ext{α}}$-attractor inflation over monomial inflation.

Contribution

It introduces the study of monomial and $oldsymbol{ ext{α}}$-attractor inflation in three extra-dimensional scenarios, deriving equations and fitting observational data to assess model viability.

Findings

Monomial inflation is disfavored across all extra-dimensional models.

$oldsymbol{ ext{α}}$-attractor inflation fits current data well.

Extra-dimensional models provide more flexibility than 4D models.

Abstract

In this paper, we study two inflationary models, namely, monomial inflation and the simplest $\alpha$-attractor inflation, within extra-dimensional frameworks. We consider three extra-dimensional setups: Dark Dimension, which embeds one flat extra-dimension to explain the observed smallness of the 4D cosmological constant $\Lambda_4$; and the two Randall-Sundrum scenarios with one warped extra-dimension, namely RS1 with two branes and RS2 with one brane. We derive the corresponding Friedmann equations, compute the slow-roll parameters in each case, and we fit the experimental data for ($n_s - 1$, $\alpha$, $\Delta_s^2$, $r$), using Planck, BICEP, and ACT data. We find that monomial inflation is strongly disfavored in all scenarios, while $\alpha$-attractor inflation provides an excellent fit to current observations, with extra-dimensional setups offering additional flexibility compared to the standard 4D case.