  A dynamical model for the dark energy is presented in which the
``quintessence'' field is the axion, $a_Z$, of a spontaneously broken global
$U(1)_{A}^{(Z)}$ symmetry whose potential is induced by the instantons of a new
gauge group $SU(2)_Z$. The $SU(2)_Z$ coupling becomes large at a scale
$\Lambda_Z \sim 10^{-3} eV$ starting from an initial value $M$ at high energy
which is of the order of the Standard Model (SM) couplings at the same scale
$M$. A perspective on a possible unification of $SU(2)_Z$ with the SM will be
briefly discussed. We present a scenario in which $a_Z$ is trapped in a false
vacuum characterized by an energy density $\sim (10^{-3} eV)^4$. The lifetime
of this false vacuum is estimated to be extremely large. Other estimates
relevant to the ``coincidence issue'' include the ages of the universe when the
$a_Z$ potential became effective, when the acceleration ``began'' and when the
energy density of the false vacuum became comparable to that of (baryonic and
non-baryonic) matter. Other cosmological consequences include a possible
candidate for the weakly interacting (WIMP) Cold Dark Matter as well as a
scenario for leptogenesis. A brief discussion on possible laboratory detections
of some of the particles contained in the model will also be presented.
