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arXiv · 2601.02982

Inflation in Extra-Dimensions with one or two branes

Nicolás Bernal·Catarina Cosme·Andrea Donini·Nuria Rius
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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.

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Nicolás Bernal, Catarina Cosme, Andrea Donini, Nuria Rius. 2026-01-06. Inflation in Extra-Dimensions with one or two branes. https://arxiv.org/abs/2601.02982

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