A minimal sub-Planckian axion inflation model with large tensor-to-scalar ratio

McDonald, John (2015) A minimal sub-Planckian axion inflation model with large tensor-to-scalar ratio. Journal of Cosmology and Astroparticle Physics, 2015 (1): 018. ISSN 1475-7516

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Abstract

We present a minimal axion inflation model which can generate a large tensor-to-scalar ratio while remaining sub-Planckian. The modulus of a complex scalar field Phi with a lambda vertical bar Phi vertical bar(4) potential couples directly to the gauge field of a strongly-coupled sector via a term of the form (vertical bar Phi vertical bar/M-Pl)(m) F (F) over tilde . This generates a minimum of the potential which is aperiodic in the phase. The resulting inflation model is equivalent to a phi(4/(m+1)) chaotic inflation model. For the natural case of a leading-order portal-like interaction of the form Phi dagger Phi F (F) over tilde, the model is equivalent to a phi(4/3) chaotic inflation model and predicts a tensor-to-scalar ratio r = 16/3N = 0.097 and a scalar spectral index n(s) = 1 - 5/3N = 0.970 . The value of vertical bar Phi vertical bar remains sub-Planckian throughout the observable era of inflation, with vertical bar Phi vertical bar less than or similar to 0.01M(Pl) for N less than or similar to 60 when lambda similar to 1.