CMB targets after the latest Planck data release

Abstract

We show that a combination of the simplest $α$-attractors and KKLTI models related to Dp-brane inflation covers most of the area in the ($n_{s}$, $r$) space favored by Planck 2018. For $α$-attractor models, there are discrete targets $3α=1,2,...,7$, predicting 7 different values of $r = 12α/N^{2}$ in the range $10^{-2} \gtrsim r \gtrsim 10^{-3}$. In the small $r$ limit, $α$-attractors and Dp-brane inflation models describe vertical $β$-stripes in the ($n_{s}$, $r$) space, with $n_{s}=1-β/N$, $β=2, {5\over 3},{8\over 5}, {3\over 2},{4\over 3}$. A phenomenological description of these models and their generalizations can be achieved in the context of pole inflation. Most of the $1σ$ area in the ($n_{s}$, $r$) space favored by Planck 2018 can be covered models with $β= 2$ and $β= 5/3$. Future precision data on $n_s$ may help to discriminate between these models even if the precision of the measurement of $r$ is insufficient for the discovery of gravitational waves produced during inflation.