# Cosmology from String Theory

## TL;DR

This paper investigates a string theory-based cosmological model that explains cosmic acceleration via a quintessence field, with implications for dark matter, fundamental constants, and compatibility with observations.

## Contribution

It presents a six-dimensional supergravity model with a stabilized modulus, consistent with cosmological data, and extends it to a ten-dimensional string theory background.

## Key findings

- The model aligns qualitatively with supernova, nucleosynthesis, and CMB observations.
- The stabilized modulus acts as a source of cold dark matter, but only accounts for about 7% of it.
- The model supports a de Sitter universe with negligible variations in fundamental constants.

## Abstract

We explore the cosmological content of Salam-Sezgin six dimensional supergravity, and find a solution to the field equations in qualitative agreement with observation of distant supernovae, primordial nucleosynthesis abundances, and recent measurements of the cosmic microwave background. The carrier of the acceleration in the present de Sitter epoch is a quintessence field slowly rolling down its exponential potential. Intrinsic to this model is a second modulus which is automatically stabilized and acts as a source of cold dark matter with a mass proportional to an exponential function of the quintessence field (hence realizing VAMP models within a String context). However, any attempt to saturate the present cold dark matter component in this manner leads to unacceptable deviations from cosmological data -- a numerical study reveals that this source can account for up to about 7% of the total cold dark matter budget. We also show that (1) the model will support a de Sitter energy in agreement with observation at the expense of a miniscule breaking of supersymmetry in the compact space; (2) variations in the fine structure constant are controlled by the stabilized modulus and are negligible; (3) ``fifth''forces are carried by the stabilized modulus and are short range; (4) the long time behavior of the model in four dimensions is that of a Robertson-Walker universe with a constant expansion rate (w = -1/3). Finally, we present a String theory background by lifting our six dimensional cosmological solution to ten dimensions.