Inflaton dark matter from incomplete decay
  We show that the decay of the inflaton field may be incomplete, while
nevertheless successfully reheating the universe and leaving a stable remnant
that accounts for the present dark matter abundance. We note, in particular,
that since the mass of the inflaton decay products is field-dependent, one can
construct models, endowed with an appropriate discrete symmetry, where inflaton
decay is kinematically forbidden at late times and only occurs during the
initial stages of field oscillations after inflation. We show that this is
sufficient to ensure the transition to a radiation-dominated era and that
inflaton particles typically thermalize in the process. They eventually
decouple and freeze out, yielding a thermal dark matter relic. We discuss
possible implementations of this generic mechanism within consistent
cosmological and particle physics scenarios, for both single-field and hybrid
inflation.
