  We show that a system of bosons in a T=0 quantum field theory can present
metastable ground states with spontaneous symmetry breaking, even in the
absence of an imaginary mass term. This gives a natural explanation to the
Davis-Shellard background field \exp(-i \omega_0 t) and adds a new degree of
freedom in boson systems, with possible applications in cosmology, condensed
matter and high energy physics.
