A solution of the strong CP problem via the Peccei-Quinn mechanism
  through the Nieh-Yan modified gravity and cosmological implications
  By identifying the recently introduced Barbero-Immirzi field with the QCD
axion, the strong CP problem can be solved through the Peccei-Quinn mechanism.
A specific energy scale for the Peccei-Quinn symmetry breaking is naturally
predicted by this model. This provides a complete dynamical setting to evaluate
the contribution of such an axion to the cold dark matter content of the
Universe. Furthermore, a tight upper bound on the tensor-to-scalar ratio
production of primordial gravitational waves can be fixed, representing a
strong experimental test for this model.
