Dynamical Chern-Simons term generation at finite density
  The Chern-Simons topological term dynamical generation in the effective action is obtained at arbitrary finite density. By using the proper time method and perturbation theory it is shown that $\mu^2 = m^2$ is the crucial point for Chern-Simons. So when $\mu^2 < m^2 \mu$--influence disappears and we get the usual Chern-Simons term. On the other hand when $\mu^2 > m^2$ the Chern-Simons term vanishes because of non-zero density of background fermions. In particular for massless case parity anomaly is absent at any finite density. This result holds in any odd dimension as in abelian so as in nonabelian cases. 
A.N. Sissakian, O.Yu. Shevchenko and S.B. Solganik