C-axis Response of a High-T_(c) Superconductor with D-Density Wave Order

The microscopic origin of the pseudogap state which exists in the underdoped cuprates remains unknown. The $c$-axis properties in the pseudogap regime are particularly anomalous. We use a recently proposed model of a $d$-density wave which leads to staggered currents and the doubling of the unit cell to investigate the $c$-axis kinetic energy and the optical sum rule. The density of states expected in the model is also considered.