  Much attention has been given to a possible violation of the optical sum rule
in the cuprates, and the connection this might have to kinetic energy lowering.
The optical integral is composed of a cut-off independent term (whose
temperature dependence is a measure of the sum rule violation), plus a cut-off
dependent term that accounts for the extension of the Drude peak beyond the
upper bound of the integral. We find that the temperature dependence of the
optical integral in the normal state of the cuprates can be accounted for
solely by the latter term, implying that the dominant contribution to the
observed sum rule `violation' in the normal state is due to the finite cut-off.
This cut-off dependent term is well modeled by a theory of electrons
interacting with a broad spectrum of bosons.
