Generation of dark radiation in the bulk inflaton model

We investigate the dynamics of a bulk scalar field with various decay channels in the Randall-Sundrum infinite braneworld scenario. A bulk scalar field in this scenario has a quasi-localized mode which dominates the late-time behavior near the brane. As for this mode, an interesting point is the presence of dissipation caused by the escape of the energy in the direction away from the brane, even if the bulk scalar field does not have the interaction with the other bulk fields in the bulk and fields on the brane. We can interpret that this lost energy is transfered to the dark radiation. We show that such an effective 4-dimensional description for a bulk scalar field is valid including the various processes of energy dissipation.