A no-go for no-go theorems prohibiting cosmic acceleration in extra dimensional models

TL;DR

This paper critically examines existing no-go theorems that claim cosmic acceleration cannot be sustained in extra-dimensional models, highlighting that these theorems rely on restrictive assumptions about the metric.

Contribution

The authors identify that previous no-go theorems depend on specific metric assumptions, and without these, the theorems do not hold, challenging prior constraints on cosmic acceleration in extra dimensions.

Findings

No-go theorems depend on restrictive metric assumptions

Relaxing assumptions invalidates the no-go results

Cosmic acceleration may be possible without these constraints

Abstract

A four-dimensional effective theory that arises as the low-energy limit of some extra-dimensional model is constrained by the higher dimensional Einstein equations. Steinhardt & Wesley use this to show that accelerated expansion in our four large dimensions can only be transient in a large class of Kaluza-Klein models that satisfy the (higher dimensional) null energy condition [1]. We point out that these no-go theorems are based on a rather ad-hoc assumption on the metric, without which no strong statements can be made.