Novel Parity Violating Transport Coefficients in 2+1 Dimensions from   Holography
  We construct a 3+1 dimensional holographic model dual to a parity violating hydrodynamic system in 2+1 dimensions. Our model contains gravitational and electrodynamic Chern-Simons terms coupled to a neutral pseudo scalar $\theta$, and a potential composed of quadratic and quartic terms in $\theta$. The background is a charged black brane. We study the hydrodynamics to first order in spacetime derivatives near the probe limit of the pseudo scalar, by extracting the transport coefficients from the scalar, vector, and tensor modes of bulk perturbations. We study two mechanisms for breaking the parity of the boundary fluid: the parity is either spontaneously broken by the nonzero vev of the dual pseudo scalar operator, or by the pseudo scalar source on the boundary. The resulting transport coefficients have unusual behaviors compared to those in ordinary materials. 
Jiunn-Wei Chen, Shou-Huang Dai, Nien-En Lee, Debaprasad Maity
hep-th