Peaky Production of Light Dark Photon Dark Matter

TL;DR

This paper proposes a novel mechanism for producing light dark photon dark matter with a peaky spectrum during inflation, evading isocurvature constraints, and predicts detectable gravitational waves.

Contribution

It introduces a new production method involving a spectator scalar field during inflation, enabling dark photon dark matter creation over a wide mass range with observable gravitational waves.

Findings

Dark photons with masses down to 10^{-13} eV can be produced.

The spectrum of dark photons is peaky, avoiding isocurvature constraints.

Fluctuations generate gravitational waves detectable by future experiments.

Abstract

We explore a mechanism to produce a light dark photon dark matter through a coupling between the dark photon field and a spectator scalar field which plays no role in the inflationary expansion of the Universe while rolling down its potential during the inflation. The motion of the spectator field efficiently produces dark photons with large wavelengths which become non-relativistic before the time of matter-radiation equality. The spectrum of the wavelengths is peaky so that the constraint from the isocurvature perturbation can be evaded. The correct relic abundance is then achieved over a wide range of the dark photon mass down to $10^{-13} \ \text{eV}$. Our mechanism favors high-scale inflation models which can be tested in future observations. Furthermore, fluctuations of the dark photon field during inflation produce gravitational waves detectable at future space-based interferometers and/or pulsar timing array experiments.