Observational constraints on Hyperinflation

Abstract: We study a Hyperinflation model involving a field doublet on a hyperbolic field-space manifold and an exponential potential, providing a concise treatment of the evolution of the entropic and adiabatic perturbations around the homogeneous hyperbolic attractor solution. We find that the adiabatic spectral index narrows down the admissible values of the potential's slope to a very small region, severely restricting the state space of the allowed background solutions.