Brane Cosmology from Heterotic String Theory

TL;DR

This paper explores brane cosmologies derived from heterotic string theory, demonstrating solutions with inflationary behavior, localized gravity, and a time-varying gravitational constant, aligning with recent cosmological observations.

Contribution

It introduces new brane cosmology solutions within heterotic string theory incorporating higher curvature corrections, with a natural inflationary internal scale and variable gravitational constant.

Findings

Internal four-dimensional scale factor exhibits exponential De-Sitter inflation.

Gravity is localized on the brane with a finite effective Planck mass.

The four-dimensional gravitational constant varies with time, matching observational data.

Abstract

We consider brane cosmologies within the context of five-dimensional actions with O(a') higher curvature corrections. The actions are compatible with bulk string amplitude calculations from heterotic string theory. We find wrapped solutions that satisfy the field equations in an approximate but acceptable manner given their complexity, where the internal four-dimensional scale factor is naturally inflating, having an exponential De-Sitter form. The temporal dependence of the metric components is non-trivial so that this metric cannot be factored as in a conformally flat case. The effective Planck mass is finite and the brane solutions localize four-dimensional gravity, while the four-dimensional gravitational constant varies with time. The Hubble constant can be freely specified through the initial value of the scalar field, to conform with recent data.