  We develop a new regularization method for the stress-energy tensor and the
two-point function of free quantum scalar fields propagating in cosmological
spacetimes. We proceed by extending the adiabatic regularization scheme with
the introduction of two additional mass scales. By setting them to the order of
the physical scale of the studied scenario, we obtain ultraviolet-regularized
quantities that do not distort the power spectra amplitude at the infrared
scales amplified by the expansion of the universe. This is not ensured by the
standard adiabatic approach. We also show how our proposed subtraction terms
can be interpreted as a renormalization of coupling constants in the Einstein
equations. We finally illustrate our proposed regularization method in two
scenarios of cosmological interest: de Sitter inflation and geometric
reheating.
