Scalar overproduction in standard cosmology and predictivity of non-thermal dark matter

TL;DR

This paper investigates how stable scalar particles produced in the early universe can lead to overproduction of dark matter, highlighting the impact of quantum gravity effects on the predictability of non-thermal dark matter models.

Contribution

It provides new constraints on scalar mass scales and emphasizes the significance of quantum gravity-induced operators in dark matter abundance predictions.

Findings

Quantum gravity operators can cause overproduction of dark relics.

Constraints on scalar mass scales are derived from early universe production.

Predictivity of non-thermal dark matter models is challenged by quantum gravity effects.

Abstract

Stable scalars can be copiously produced in the Early Universe even if they have no coupling to other fields. We study production of such scalars during and after (high scale) inflation, and obtain strong constraints on their mass scale. Quantum gravity-induced Planck-suppressed operators make an important impact on the abundance of dark relics. Unless the corresponding Wilson coefficients are very small, they normally lead to overproduction of dark states. In the absence of a quantum gravity theory, such effects are uncontrollable, bringing into question predictivity of many non-thermal dark matter models. These considerations may have non-trivial implications for string theory constructions, where scalar fields are abundant.