Topological Effects in Medium

Abstract

Two closely related topological phenomena are studied at finite density and temperature. These are chiral anomaly and Chern--Simons term. It occurs that the chiral anomaly doesn&#39;t depend on density and temperature. Chern-Simons term appearance in even dimensions is studied under two types of constraints: chiral and usual charges conservation. In odd dimensions, by using different methods it is shown that $μ^2 = m^2$ is the crucial point for Chern--Simons at zero temperature. So when $μ^2 < m^2$ $μ$--influence disappears and we get the usual Chern-Simons term. On the other hand, when $μ^2 > m^2$ the Chern-Simons term vanishes because of non--zero density of background fermions. The connection between parity anomalous Chern-Simons in odd dimension and chiral anomaly in even dimension is established at arbitrary density and temperature. These results hold in any dimension as in abelian, so as in nonabelian cases.