  A new mechanism of parity breakdown in a spinor Bose gas is predicted; it
causes a single-mode state of polaritons to be spontaneously divided into
different polarization domains which annihilate each other at the interface
areas. In a polariton wire, such interface is a dark soliton that can run in
space without dissipation. In a planar cavity, quantized vortices arise in
which phase difference of orthogonally polarized components makes one complete
turn around the core. Coupled vortex-antivortex pairs and straight filaments
can form in analogy to Bose-Einstein condensates and superconductors. However,
the rotational symmetry is broken even for individual vortices, which makes
them interact on a large scale and form internally ordered structures. These
states come into being under resonant excitation if the spin coupling rate
significantly exceeds the decay rate.
