  Vacuum effects in (2+1)-dimensional quantum electrodynamics (QED) with the
topological Chern-Simons term are considered. The photon polarization operator
is studied and the decay rate for the electron-positron photoproduction is
presented as a function of the photon energy and external field strength. The
radiatively induced electron mass shift in an external magnetic field is
investigated. The electron self-energy in topologically massive (2+1)-QED at
finite temperature and density is studied. The parity breaking part of the
Yang-Mills action in the framework of the $SU(2)\times U(1)$ gauge field model
at finite temperature is considered.
