Cosmic acceleration from string induced Galileons

TL;DR

This paper explores cosmological solutions in a string-derived gravity theory, revealing scenarios of cosmic acceleration and bouncing universes, with implications for the number of noncompact dimensions and stability conditions.

Contribution

It provides the first exact solutions to lower-dimensional cosmological models derived from a string-inspired Horndeski theory, including models with cosmic acceleration and stability considerations.

Findings

Unaltered duality symmetry in string frame leads to bouncing and pre-Big Bang solutions.

Exact models exhibit cosmic acceleration depending on noncompact dimensions.

Stability requirements suggest including a dilaton potential.

Abstract

It has been shown a specific Horndeski theory of gravity arises from a consistent Kaluza-Klein reduction of the gravi-dilaton sector of the low-energy effective heterotic string action with a first $\alpha'$ correction. Here we provide a first investigation of the cosmological solutions to the lower dimensional theory by constructing exact solutions to the field equations in various frames. At tree level, in string frame, we find the duality symmetry of the parent theory is unaltered by dimensional reduction, leading to standard bouncing and pre-Big Bang scenario solutions. For $\alpha'\neq0$, we uncover exact models exhibiting cosmic acceleration, where we find interesting physics concerning the number of noncompact dimensions. Certain stability requirements demand the inclusion of a dilaton potential.