Small Field Inflation and the Spectral Index

Understand

It is sometimes stated that $n_s = 0.98$ in hybrid inflation; sometimes that it predicts $n_s >1$.

• A number of authors have consider aspects of Planck scale corrections and argued that they affect these predictions.
• Here we consider these systematically, describing the situations which can yield $n_s =0.96$, and the extent to which this result requires additional tuning.