| Details: |
We will revise the proposed mechanism for producing non-thermal dark
photon dark matter at the end of inflation. A tachyonic instability
induced by a rolling inflaton leads to the coherent production of dark
(abelian) gauge bosons with a peak in the power spectrum corresponding
to the Hubble scale at the end of inflation. As the Universe expands
after inflation the dark photons redshift and, at some point in their
cosmic evolution, they obtain a mass. We focus in particular on the case
where the dark photons are relativistic at the time their mass is
generated, and examine the associated cosmic evolution to compute the
relic abundance today. In addition, dark electron-positron pairs may
also be produced close to the end of inflation via the Schwinger effect.
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, and they could account
for the dark matter abundance today. This mechanism is viable even when
(purely) gravitational particle production is negligible. Thus the final
dark matter relic abundance is determined only by the initial
inflationary Schwinger production and redshifting after reheating. |