Transport properties in the d-density wave state: Wiedemann-Franz law

We study the Wiedemann-Franz (WF) law in the d-density wave (DDW) model. Even though the opening of the DDW gap $(W_0)$ profoundly modifies the electronic density of states and makes it dependent on energy, the value of the WF ratio at zero temperature (T=0) remains unchanged. However, neither electrical nor thermal conductivity display universal behavior. For finite temperature, with T greater than the value of the impurity scattering rate at zero frequency $\gamma (0)$ i.e. $\gamma (0)<T\ll W_0$, the usual WF ratio is obtained only in the weak scattering limit. For strong scattering there are large violations of the WF law.