Momentum dissipation and holographic transport without self-duality
  We implement the momentum dissipation introduced by spatial linear axionic fields in a holographic model without self-duality, broke by Weyl tensor coupling to Maxwell field, and study its response. It is found that for the positive Weyl coupling parameter $\gamma>0$, the momentum dissipation characterized by parameter $\hat{\alpha}$ drives the boundary conformal field theory (CFT), in which the conductivity exhibits a peak at low frequency, into the incoherent metallic phase with a dip, which is away from CFT due to the introduction of axionic fields. While for $\gamma<0$, an oppositive scenario is found. Our present model provides a possible route toward the problem that which sign of $\gamma$ is the correct description of the CFT of boson Hubbard model. In addition, we also investigate the DC conductivity, diffusion constant and susceptibility. We find that for each of these observables there is a specific value of $\hat{\alpha}$, for which these observables are independent of $\gamma$. Finally, the electromagnetic (EM) duality is also studied and we find that there is also a specific value of $\hat{\alpha}$, for which the particle-vortex duality related by the change of the sign of $\gamma$ in the boundary theory holds better than for other values of $\hat{\alpha}$. 
Jian-Pin Wu
hep-th gr-qc