  We consider D-term inflation for small couplings of the inflaton to matter
fields. Standard hybrid inflation then ends at a critical value of the inflaton
field that exceeds the Planck mass. During the subsequent waterfall transition
the inflaton continues its slow-roll motion, whereas the waterfall field
rapidly grows by quantum fluctuations. Beyond the decoherence time, the
waterfall field becomes classical and approaches a time-dependent minimum,
which is determined by the value of the inflaton field and the self-interaction
of the waterfall field. During the final stage of inflation, the effective
inflaton potential is essentially quadratic, which leads to the standard
predictions of chaotic inflation. The model illustrates how the decay of a
false vacuum of GUT-scale energy density can end in a period of `chaotic
inflation'.
