Disappearing Inflaton Potential via Heavy Field Dynamics
  We propose a possibility that the inflaton potential is significantly
modified after inflation due to heavy field dynamics. During inflation there
may be a heavy scalar field stabilized at a value deviated from the low-energy
minimum. As the heavy field moves to the low-energy minimum, the inflaton
potential could be significantly modified. In extreme cases, the inflaton
potential vanishes and the inflaton becomes almost massless at some time after
inflation. Such transition of the inflaton potential has interesting
implications for primordial density perturbations, reheating, creation of
unwanted relics, dark radiation, and experimental search for light degrees of
freedom. To be concrete, we consider a chaotic inflation in supergravity where
the inflaton mass parameter is promoted to a modulus field, finding that the
inflaton becomes stable after the transition and contributes to dark matter.
Another example is the new inflation by the MSSM Higgs field which acquires a
large expectation value just after inflation, but it returns to the origin
after the transition and settles down at the electroweak vacuum. Interestingly,
the smallness of the electroweak scale compared to the Planck scale is directly
related to the flatness of the inflaton potential.
