The creation of radiation and the relic of inflaton potential
  Recently, we have performed research on the subject of the cosmological constant problem. The scenario is based on two postulates for inflationary theory: one is that inflaton $\phi$ can interact with radiation (relativistic particles); the other is that radiation will be created continuously during and after the epoch of inflation. According to these postulates and from a "macroscopic perspective", we discover that radiation can be viewed as a product of the interaction between $\dot{\phi}$ and some "effective kinetic frictional force" that exists in inflaton dynamics. Deducing and surmising from "effective friction", we obtain conclusions of two special types of expanding universe: A Type I universe will finally enter an expanding course after a special time $t_{*}$ with uniformly rolling $\dot{\phi}(t_{*})$ due to the balance between $V^{'}(\phi(t))$, 3H(t)\dot{\phi}(t_{*}) and the "effective kinetic frictional force". In this result, the expanding course will see particles created continuously. Additionally, for a Type II universe, $\phi$ will be at rest after $t_{r}$ inside a region named the "stagnant zone" that is formed by the "maximum effective static frictional force". Consistent with this, inflaton potential will survive as a relic $V(\phi(t_{r}))$, playing the role of the effective cosmological constant $\Lambda$ . 
Yu-Chung Chen
gr-qc hep-th