Opening up extra dimensions at ultra-large scales

TL;DR

This paper demonstrates that in models with infinite extra dimensions, gravity can behave as five-dimensional at both very short and very long scales, challenging the conventional view that extra dimensions are only detectable at short distances.

Contribution

It introduces a five-dimensional brane model where gravity remains five-dimensional at all scales, including cosmological distances, without requiring fine-tuning.

Findings

Gravity is five-dimensional at both microscopic and cosmological scales.

Four-dimensional gravity is recovered at intermediate scales.

The model fits observational constraints without fine-tuning.

Abstract

The standard picture of viable higher-dimensional theories is that extra dimensions manifest themselves at short distances only, their effects being negligible at scales larger than some critical value. We show that this is not necessarily true in models with infinite extra dimensions. As an example, we consider a five-dimensional scenario with three 3-branes in which gravity is five-dimensional both at short {\it and} very long distance scales, with conventional four-dimensional gravity operating at intermediate length scales. A phenomenologically acceptable range of validity of four-dimensional gravity extending from microscopic to cosmological scales is obtained without strong fine-tuning of parameters.