  The recent three-year WMAP data selects large-field models with certain
power-law potentials and small-field models for all power-law potentials as
consistent inflation models. We study the large-field and small-field inflation
model with a quadratic and a quartic potential within the framework of quantum
field theory in an expanding Friedmann-Robertson-Walker universe. We find that
quantum fluctuations in the small-field model lead to a significant
contribution to the effective potential and may have non-negligible effects on
the slow-roll parameters predicted by classical theory.
