In this work, the authors have shown that the inflaton scalar field, responsible for the period of accelerated expansion in the early Universe known as inflation, can also naturally account for the cold dark matter in the present Universe, within the framework of warm inflation. Hence, this provides a unified explanation to both inflaton and dark matter with a single scalar field.
In this scenario, the symmetries of the underlying quantum field theory model allow the inflaton field to dissipate its energy into the cosmic heat bath during inflation, thus keeping it at a high temperature. However, after inflation the temperature drops bellow the mass of the particles coupled to the inflaton, and dissipative effects become exponentially suppressed, preventing the inflaton from decaying completely. The stable inflaton remnant behaves as a pressureless, non-relativistic fluid that is very weakly coupled to the known particles, thus acting as cold dark matter.