Unifying inflation and dark matter with the Peccei-Quinn field: observable axions and observable tensors

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A model of high scale inflation is presented where the radial part of the Peccei-Quinn (PQ) field with a non-minimal coupling to gravity plays the role of the inflaton, and the QCD axion is the dark matter. A quantum fluctuation of O(H/2π) in the axion field will result in a smaller angular fluctuation if the PQ field is sitting at a larger radius during inflation than in the vacuum. This changes the effective axion decay constant, fₐ, during inflation and dramatically reduces the production of isocurvature modes. This mechanism opens up a new window in parameter space where an axion decay constant in the range 10¹² GeV fₐ 10¹⁵ GeV is compatible with observably large r. The exact range allowed for fₐ depends on the efficiency of reheating. This model also predicts a minimum possible value of r=10⁻³. The new window can be explored by a measurement of r possible with Spider and the proposed CASPEr experiment search for high fₐ axions.