  The regularization of the CMB power spectrum is an important issue of
cosmology. Most approaches assume that there is no need to regularize the power
spectrum, while Parker advocated the new regularization approach for the power
spectrum in 2007: the adiabatic regularization, which was originally developed
for particle creation in curved spacetime. This thesis focuses on this issue,
especially concerning adiabatic subtraction terms. The subtraction terms for
minimally coupled slow-roll inflation are well known. We extend the view to
more generic inflation models, and derive the subtraction terms for k-inflation
models. Via the method of Urakawa-Starobinsky, we consider the time development
of the subtraction term at late times. We also consider the non-minimally
coupled case, and show that the adiabatic regularization is independent of the
frame: Jordan or Einstein frames.
