Torsional response of relativistic fermions in $2+1$ dimensions

We consider the equilibrium partition function of an ideal gas of Dirac fermions minimally coupled to torsion in $2+1$ dimensions. We show that the energy-momentum tensor reproduces the Hall viscosity and other parity violating terms of first order in the torsion. We also consider the modifications of the constitutive relations, and classify the corresponding susceptibilities. An entropy current consistent with zero production of entropy in equilibrium is constructed.