The QCD Nature of Dark Energy

The origin of the observed dark energy could be explained entirely within the standard model, with no new fields required. I will show how the low-energy sector of the chiral QCD Lagrangian, once embedded in a spacetime with non-trivial topology, gives rise to a cosmological vacuum energy density which can be presented entirely in terms of QCD parameters and the Hubble constant, and whose numerical value is astonishingly close to the observed value today. The QCD Veneziano ghost (responsible for the solution of the axial U(1) problem) plays a crucial role in the computation of the vacuum energy, because the ghosts properties at very large but finite distances slightly deviate from their infinite volumne Minkowski values. After a detailed review of the mechanism in a non-expanding univese, I will describe our attempts to understand the dynamics of the ghost field in a FLRW universe, and mention several possible ways (primarily cosmological) for this proposal to be tested.