Isocurvature Perturbations and Non-Gaussianity of Gravitationally Produced Nonthermal Dark Matter

TL;DR

This paper explores how gravitationally produced nonthermal dark matter can generate observable local non-Gaussianities without conflicting with isocurvature constraints, even if they constitute a small fraction of dark matter.

Contribution

It demonstrates that nonthermal dark matter from gravitational production can produce detectable non-Gaussian signals while satisfying existing isocurvature bounds.

Findings

Nonthermal dark matter can generate observable non-Gaussianities.

Such dark matter can be consistent with isocurvature constraints.

Detectable signals are possible even with a small dark matter fraction.

Abstract

Gravitational particle production naturally occurs during the transition from the inflationary phase to the non-inflationary phase. If the particles are stable and very weakly interacting, they are natural nonthermal dark matter candidates. We show that such nonthermal dark matter particles can produce local non-Gaussianities large enough to be observed by ongoing and near future experiments without being in conflict with the existing isocurvature bounds. Of particular interest is the fact that these particles can be observable through local non-Gaussianities even when they form a very small fraction of the total dark matter content.