Bounds on Scalar Masses in Theories of Moduli Stabilization

TL;DR

This paper explores bounds on scalar moduli masses in string theories, emphasizing their cosmological implications, especially for dark matter production, and suggests that at least one modulus is typically lighter than the gravitino, affecting early universe cosmology.

Contribution

It provides a conjecture that in stabilized string theories, a light modulus exists, influencing the non-thermal history of the universe and dark matter production mechanisms.

Findings

Moduli dominated the pre-BBN universe.

Gravitino mass should be at least ~30 TeV.

Wino-like LSPs can account for dark matter.

Abstract

In recent years it has been realised that pre-BBN decays of moduli can be a significant source of dark matter production, giving a `non-thermal WIMP miracle' and substantially reduced fine-tuning in cosmological axion physics. We study moduli masses and sharpen the claim that moduli dominated the pre-BBN Universe. We conjecture that in any string theory with stabilized moduli there will be at least one modulus field whose mass is of order (or less than) the gravitino mass. Cosmology then generically requires the gravitino mass not be less than about 30 TeV and the cosmological history of the Universe is non-thermal prior to BBN. Stable LSP's produced in these decays can account for the observed dark matter if they are `wino-like.' We briefly consider implications for the LHC, rare decays, and dark matter direct detection and point out that these results could prove challenging for models attempting to realize gauge mediation in string theory.