Dark Matter and Dark Energy from the solution of the strong CP problem
  The Peccei Quinn (PQ) solution of the strong CP problem requires the existence of axions, which are a viable candidate for Dark Matter. Here we show that, if the Nambu Goldstone potential of the PQ model is replaced by a potential V(|\Phi|) admitting a tracker solution, the scalar field |\Phi| can account for Dark Energy, while the phase of \Phi yields axion Dark Matter. Such Dark Matter and Dark Energy turn out to be weakly coupled. If V is a SUGRA potential, the model essentially depends on a single parameter, the energy scale \Lambda. Once we set \Lambda \simeq 10^{10} GeV, at the quark--hadron transition, |\Phi| naturally passes through values suitable to solve the strong CP problem, later growing to values providing fair amounts of Dark Matter and Dark Energy. In this model, the linear growth factor, from recombination to now, is quite close to \LambdaCDM. The selected \Lambda value can be an indication of the scale where the soft breaking of SUSY occurred. 
Roberto Mainini and Silvio A. Bonometto