  In a wide class of three-dimensional Abelian gauge theories with a bare
Chern-Simons term, the Lorentz invariance is spontaneously broken by dynamical
generation of a non-vanishing magnetic field. A detailed computation of an
energy density of the true vacuum is given. The originally massive photon
becomes massless, fulfilling the role of a Nambu-Goldstone boson associated
with the spontaneous breaking of the Lorentz invariance.
