Completely Dark Photons from Gravitational Particle Production During Inflation

TL;DR

This paper calculates the production of dark photons during inflation via gravitational particle production, showing it can generate dark matter across a wide mass range without requiring coupling to standard-model particles.

Contribution

It provides a detailed calculation of gravitational particle production of dark photons during inflation, covering their evolution through reheating and broad mass spectrum.

Findings

Dark photons can be produced as dark matter with masses from micro-electron volts to 10^{14} GeV.

Gravitational particle production is independent of dark photon coupling to standard-model particles.

Plausible scenarios for dark photon dark matter production during inflation are identified.

Abstract

Starting with the de Broglie--Proca Lagrangian for a massive vector field, we calculate the number density of particles resulting from gravitational particle production (GPP) during inflation, with detailed consideration to the evolution of the number density through the reheating. We find plausible scenarios for the production of dark-photon dark matter of mass in a wide range, as low as a micro-electron volt to $10^{14}$ GeV. Gravitational particle production does not depend on any coupling of the dark photon to standard-model particles.