Oxidised cosmic acceleration

TL;DR

This paper proves new no-go theorems showing that constructing flat, accelerating universes from higher-dimensional warped compactifications generally violates energy conditions, especially for de Sitter expansion, with implications for cosmological models.

Contribution

The authors establish improved no-go theorems that weaken energy condition assumptions and include time-dependent compactifications, extending previous results to non-de Sitter acceleration.

Findings

De Sitter expansion violates higher-dimensional NEC under specific conditions.

Threshold w values determine whether accelerated expansion is transient or violates energy conditions.

Experimental measurements of w can distinguish models satisfying or violating energy conditions.

Abstract

We give detailed proofs of several new no-go theorems for constructing flat four-dimensional accelerating universes from warped dimensional reduction. These new theorems improve upon previous ones by weakening the energy conditions, by including time-dependent compactifications, and by treating accelerated expansion that is not precisely de Sitter. We show that de Sitter expansion violates the higher-dimensional null energy condition (NEC) if the compactification manifold M is one-dimensional, if its intrinsic Ricci scalar R vanishes everywhere, or if R and the warp function satisfy a simple limit condition. If expansion is not de Sitter, we establish threshold equation-of-state parameters w below which accelerated expansion must be transient. Below the threshold w there are bounds on the number of e-foldings of expansion. If M is one-dimensional or R everywhere vanishing, exceeding the bound implies the NEC is violated. If R does not vanish everywhere on M, exceeding the bound implies the strong energy condition (SEC) is violated. Observationally, the w thresholds indicate that experiments with finite resolution in w can cleanly discriminate between different models which satisfy or violate the relevant energy conditions.