Inflation from Extra Dimensions

TL;DR

This paper proposes a higher-dimensional gravity model where contracting extra dimensions induce inflation in the observable three dimensions, linking it to dilaton-driven cosmologies but facing similar exit challenges.

Contribution

It introduces a simple higher-dimensional framework where contracting extra dimensions drive inflation, connecting it to dilaton cosmologies and highlighting the graceful exit problem.

Findings

Higher-dimensional contraction leads to 3D inflation

Dimensional reduction yields a dynamical Planck mass

The model faces the graceful exit problem

Abstract

A gravity-driven inflation is shown to arise from a simple higher dimensional universe. In vacuum, the shear of $n>1$ contracting dimensions is able to inflate the remaining three spatial dimensions. Said another way, the expansion of the 3-volume is accelerated by the contraction of the $n$-volume. Upon dimensional reduction, the theory is equivalent to a four dimensional cosmology with a dynamical Planck mass. A connection can therefore be made to recent examples of inflation powered by a dilaton kinetic energy. Unfortunately, the graceful exit problem encountered in dilaton cosmologies will haunt this cosmology as well.