Theory of THz Conductivity in the Pseudogap Phase of the Cuprates: A   Pre-Formed Pair Perspective
  In this paper we deduce transport properties in the presence of a pseudogap associated with precursor superconductivity. Our theoretical analysis is based on the widely adopted self energy expression reflecting this normal state gap, which has appeared in interpretations of photoemission and in other experiments. Thus, it should be generally applicable. Here we address THz conductivity $\sigma (\omega) = \sigma_1(\omega) + i \sigma_2(\omega)$ measurements in the underdoped high temperature superconductors and arrive at reasonable agreement between theory and recent experiment for both $\sigma_1$ and $\sigma_2$ above and below $T_c$. 
Dan Wulin and V. Mishra and K. Levin
cond-mat.supr-con