Super heavy dark matter from inflationary Schwinger production

Abstract

We consider a simple setup with a dark sector containing dark electrons charged under an abelian $U(1)_D$ gauge symmetry. We show that if the massless dark photon associated to the $U(1)_D$ is produced during inflation in such a way as to form a classical dark electric field, then dark electron-positron pairs are also produced close to the end of inflation via the Schwinger effect even if they are very massive. For large enough dark electric force, dark electrons with masses larger than the Hubble scale can be produced which are non-relativistic at production and throughout their cosmic evolution. They can account for the dark matter abundance today for masses in the range $\sim$ 100 GeV to $10^{17}$ GeV and up to six orders of magnitude larger than the Hubble scale at the end of inflation where purely gravitational production is exponentially suppressed. We examine the regime where the dark electrons do not thermalize with the dark photons throughout their cosmic history and assume negligible kinetic mixing with the visible $U(1)$ so they remain decoupled from the Standard Model thermal bath as well. Thus the final dark matter relic abundance is determined only by the initial inflationary Schwinger production and redshifting after reheating.