Non-standard hierarchies of the runnings of the spectral index in inflation

Abstract

Recent analyses of cosmic microwave background surveys have revealed hints that there may be a non-trivial running of the running of the spectral index. If future experiments were to confirm these hints, it would prove a powerful discriminator of inflationary models, ruling out simple single field models. We discuss how isocurvature perturbations in multi-field models can be invoked to generate large runnings in a non-standard hierarchy, and find that a minimal model capable of practically realising this would be a two-field model with a non-canonical kinetic structure. We also consider alternative scenarios such as variable speed of light models and canonical quantum gravity effects and their implications for runnings of the spectral index.

10 pages, conference proceedings for VARCOSMOFUN'16, submitted to special issue "Varying Constants and Fundamental Cosmology" in Universe

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• Higher-order extension of Starobinsky inflation: initial conditions, slow-roll regime, and reheating phase
• Adiabatic and isocurvature perturbations in extended theories with kinetic couplings