Dark matter from gravitational particle production at reheating

Abstract

We show that curvature induced particle production at reheating generates adiabatic dark matter if there are non-minimally coupled spectator scalars weakly coupled to visible matter. The observed dark matter abundance implies an upper bound on spectator masses $m$ and non-minimal coupling values $\xi$. For example, assuming quadratic inflation, instant reheating and a single spectator scalar with only gravitational couplings, the observed dark matter abundance is obtained for $m\sim 0.1$ GeV and $\xi \sim 1$. Larger mass and coupling values of the spectator are excluded as they would lead to overproduction of dark matter.

Comments: 10 pages, 1 figure. v2: updated references. v3: substantial modifications, results and conclusions partially changed but bounds on spectator fields almost unaffected. New title. v4: expanded discussion, accepted for publication in JCAP