  A metastable phase has important physical implications, since it may form
vacuum bubbles detectable experimentally, whereas an unstable vacuum instantly
explodes. It is well known, due to chiral symmetry breaking, there are at least
two very different QCD vacua. At T=0 and in the true vacuum, the scalar and
pseudoscalar, or the vector and axial vector are not degenerate, and in the
chiral limit, the pseudoscalar ground states are Goldstone bosons. At T=0 the
chiral invariant vacuum is an unstable vacuum, decaying through an infinite
number of scalar and pseudoscalar tachyons. Moreover QCD vacuum replicas, an
infinite tower of excited vacuum solutions, which energy density lies between
the true vacuum and the chiral invariant vacuum, have been predicted in the
Coulomb gauge, due to the non-linearity of the mass gap equation with a
confining interaction. It remained to show whether the QCD replicas are
metastable or unstable. In this paper the spectrum of quark-antiquark systems,
is studied in the true vacuum and in the first excited QCD replicas. The mass
gap equation for the vacua and the Salpeter-RPA equation for the mesons are
solved for a simple chiral invariant and confining quark model approximating
QCD in the Coulomb gauge. We find no tachyons, thus showing the QCD replicas in
our approach is indeed metastable. Moreover the energy spectra of the mesonic
quark-antiquark systems in the first replicas are close to the one of the true
vacuum.
