Shadow vacuum alignment and dark energy

Understand

In a recent model of dark energy (with several phenomenological consequences), the universe is assumed to be trapped in a false vacuum with an energy density of the order of (10^{-3} eV)^4, mimicking the presently successful $\Lambda CDM$ scenario.

• This involves a new gauge group SU(2)_Z, {\em the shadow sector}, which becomes strong at a scale $\Lambda_Z \sim 10^{-3} eV$.
• The model is described by the SU(2)_Z instanton-induced potential of an axion-like scalar field, a_Z, with two degenerate vacuua.
• The false (metastable) vacuum appears as a result of an phenomenological (ad-hoc) soft breaking term linear in a_Z which explicitely breaks that degeneracy.