  Dark photons are a theorized massive spin-1 particle which can be produced
via various mechanisms, including cosmological gravitational particle
production (GPP) in the early universe. In this work, we extend previous
results for GPP of dark photons to include nonminimal couplings to gravity. We
find that nonminimal couplings can induce a ghost instability or lead to
runaway particle production at high momentum and discuss the constraints on the
parameter space such that the theory is free of instabilities. Within the
instability-free regime we numerically calculate the particle production and
find that the inclusion of nonminimal couplings can lead to an enhancement of
the particle number. As a result, GPP of nonminimally coupled dark photons can
open the parameter space for production of a cosmological relevant relic
density (constituting all or part of the dark matter) as compared to the
minimally-coupled theory. These results are independent of the choice of
inflation model, which we demonstrate by repeating the analysis for a class of
rapid-turn multi-field inflation models.
