Accelerating cosmologies from compactification with a twist

TL;DR

This paper shows that by including geometric twists in time-dependent compactifications of string/M-theory, one can achieve transient or arbitrarily prolonged periods of accelerated cosmology in four dimensions.

Contribution

It introduces a novel mechanism involving geometric twists in compactification to produce accelerated cosmologies from higher-dimensional vacuum Einstein equations.

Findings

Acceleration can be achieved with Ricci-flat internal spaces using twists.

Including hyperbolic spaces and twists extends acceleration duration.

Acceleration periods can be made arbitrarily long with specific internal geometries.

Abstract

It is demonstrated by explicit solutions of the (4+n)-dimensional vacuum Einstein equations that accelerating cosmologies in the Einstein conformal frame can be obtained by a time-dependent compactification of string/M-theory, even in the case that internal dimensions are Ricci-flat, provided one includes one or more geometric twists. Such acceleration is transient. When both compact hyperbolic internal spaces and geometric twists are included, however, the period of accelerated expansion may be made arbitrarily large.