Unificaxion
  Dark matter, gauge coupling unification, and the strong CP problem find a common and simple solution (in the absence of naturalness) within axion models. We show that such solution, even without specifying the details of the model implementation, makes testable predictions for the experimentally measurable axion parameters: the axion mass and its coupling to photons. 
Gian F. Giudice, Riccardo Rattazzi, Alessandro Strumia
hep-ph