# Evidence for Inflation in an Axion Landscape [CL]

We discuss inflation models within supersymmetry and supergravity frameworks which possess an axionic landscape and a shift symmetry which is broken by non-perturbative symmetry breaking terms in the superpotential. The proposed models constitute consistent inflation for the following reasons: The inflation potential arises dynamically with stabilized saxions, the axion decay constant can lie in the sub-Planckian region, and consistency with the Planck data is achieved. The axion landscape consisting of $m$ axion pairs is assumed with the axions in each pair having opposite charges. A fast roll–slow roll splitting mechanism for the axion potential is proposed which is realized with a special choice of the axion basis. In this basis the $2m$ coupled equations split into $2m-1$ equations which enter in the fast roll and there is one unique linear combination of the $2m$ fields which controls the slow roll and thus the power spectrum of curvature and tensor perturbations. It is shown that a significant part of the parameter space exists where inflation is successful, i.e., $N_{\rm pivot} = {[50, 60]}$, the spectral index $n_s$ of curvature perturbations, and the ratio $r$ of the power spectrum of tensor perturbations and curvature perturbations, lie in the experimentally allowed regions given by the Planck experiment. Further, it is shown that the model allows for a significant region of the parameter space where the effective axion decay constant can lie in the sub-Planckian domain. An analysis of the tensor spectral index $n_t$ is also given and the future experimental data which constraints $n_t$ will further narrow down the parameter space of the proposed inflationary models.

P. Nath and M. Piskunov
Wed, 6 Dec 17
29/71