We treat a model with orbitals on the copper and oxygen sites and hopping between them. In the limit of infinite U on the Cu site, the problem is treated using the slave boson method. In the presence of doping, we find a Fermi liquid solution with mass enhancement proportional to x-1. A new feature in the optical absorption is found with oscillator strength proportional to x. The interaction between quasi-particles via the exchange of slave bosons will be discussed.
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