Non-Abelian $S$-term dark energy and inflation
  We study the role that a cosmic triad in the generalized $SU(2)$ Proca
theory, specifically in one of the pieces of the Lagrangian that involves the
symmetric version $S_{\mu \nu}$ of the gauge field strength tensor $F_{\mu
\nu}$, has on dark energy and primordial inflation. Regarding dark energy, the
triad behaves asymptotically as a couple of radiation perfect fluids whose
energy densities are negative for the $S$ term but positive for the Yang-Mills
term. This leads to an interesting dynamical fine-tuning mechanism that gives
rise to a combined equation of state parameter $\omega \simeq -1$ and,
therefore, to an eternal period of accelerated isotropic expansion for an ample
spectrum of initial conditions. Regarding primordial inflation, one of the
critical points of the associated dynamical system can describe a prolonged
period of isotropic slow-roll inflation sustained by the $S$ term. This period
ends up when the Yang-Mills term dominates the energy density leading to the
radiation dominated epoch. Unfortunately, in contrast to the dark energy case,
the primordial inflation scenario is strongly sensitive to the coupling
constants and initial conditions. The whole model, including the other pieces
of the Lagrangian that involve $S_{\mu \nu}$, might evade the recent strong
constraints coming from the gravitational wave signal GW170817 and its
electromagnetic counterpart GRB 170817A.
