  If the initial state of the inflaton field is taken to have a thermal
distribution instead of the conventional zero particle vacuum state then the
curvature power spectrum gets modified by a temperature dependent factor such
that the fluctuation spectrum of the microwave background radiation is enhanced
at larger angles. We compare this modified cosmic microwave background spectrum
with Wilkinson microwave anisotropy probe data to obtain an upper bound on the
temperature of the inflaton at the time our current horizon crossed the horizon
during inflation. We further conclude that there must be additional e-foldings
of inflation beyond what is needed to solve the horizon problem.
