Speaker
Description
A metastable phase has important physical implications, since it may form vacuum bubbles detectable experimentally. It is well known that, due to spontaneous chiral symmetry breaking, there are two, or more, different QCD vacua. In the chiral limit, in the true vacuum, the pseudoscalar ground states are Goldstone bosons. The chiral invariant vacuum (at the top of the "Mexican hat") is an unstable vacuum decays through an infinite number of scalar and pseudoscalar tachyons. Besides, QCD vacuum replicas, an infinite tower of excited vacuum solutions, have been predicted in the Coulomb gauge. It remained to show whether the QCD replicas are metastable or unstable. We study the spectrum of quark-antiquark systems 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 model of 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.
