Estimation of gravitational production uncertainties

TL;DR

This paper investigates the robustness of gravitational production of scalar dark matter during inflation, showing that the mechanism can explain observed dark matter abundance across different inflationary models and parameter spaces.

Contribution

It provides a comprehensive analysis of dark matter production during inflation, demonstrating its independence from specific inflationary potentials and offering an analytic approximation for the abundance.

Findings

Dark matter abundance can be explained by gravitational production in various inflation models.

Production is largely independent of the inflationary potential within certain parameter regions.

An analytic expression for dark matter abundance as a function of coupling and mass is derived.

Abstract

Cosmological production of scalar, non-minimally coupled dark matter depends on the specifics of the inflationary model under consideration. We analyze both Starobinsky inflation and a quadratic potential, solve the full background dynamics, study pair production during inflation and reheating, and find that the observed dark matter abundance can be explained solely by this mechanism, regardless of the inflationary model. Qualitative differences between the two cases only appear for dark matter masses close to the inflationary scale. In addition, we identify a large region in parameter space in which cosmological production of dark matter is mostly independent of the chosen inflationary potential, highlighting the robustness of this dark matter production mechanism and its independence of the unknown particular details of inflation. In the region of masses lower than the scale of inflation, and sufficiently away from the conformal limit, the total comoving number density of produced particles becomes a function of the coupling to the geometry alone. This allows us to provide an approximated analytic expression for fitting the resulting abundance.