Lyth bound of inflation with a tilt

We provide strong evidence for universality of the inflationary field range: given an accurate measurement of (nₛ,r), one can infer Δφ in a model-independent way in the sub-Planckian regime for a range of universality classes of inflationary models. Both the tensor-to-scalar ratio as well as the spectral tilt are essential for the field range. Given the Planck constraints on nₛ, the Lyth bound is strengthened by two orders of magnitude: whereas the original bound gives a sub-Planckian field range for r2×10^-3, we find that nₛ=0.96 brings this down to r2×10^-5.