Anisotropic Inflation and the Origin of Four Large Dimensions

TL;DR

This paper presents a higher-dimensional inflationary model where three large spatial dimensions emerge naturally while extra dimensions stay small, using a self-interacting form field without needing additional stabilization mechanisms.

Contribution

It introduces a novel inflationary scenario in (4+d)-dimensional gravity with a self-interacting d-form, explaining the growth of three dimensions and stabilization of extra dimensions without radion stabilization.

Findings

Stable solutions exist for flat and negatively curved extra dimensions.

The model naturally suppresses CMB anisotropies due to higher-dimensional effects.

The mechanism ends inflation, heats the universe, and avoids equivalence principle violations.

Abstract

In the context of (4+d)-dimensional general relativity, we propose an inflationary scenario wherein 3 spatial dimensions grow large, while d extra dimensions remain small. Our model requires that a self-interacting d-form acquire a vacuum expectation value along the extra dimensions. This causes 3 spatial dimensions to inflate, whilst keeping the size of the extra dimensions nearly constant. We do not require an additional stabilization mechanism for the radion, as stable solutions exist for flat, and for negatively curved compact extra dimensions. From a four-dimensional perspective, the radion does not couple to the inflaton; and, the small amplitude of the CMB temperature anisotropies arises from an exponential suppression of fluctuations, due to the higher-dimensional origin of the inflaton. The mechanism triggering the end of inflation is responsible, both, for heating the universe, and for avoiding violations of the equivalence principle due to coupling between the radion and matter.