CMB targets after the latest Planck data release

TL;DR

This paper demonstrates that combining simple $ ext{α}$-attractors with Dp-brane inflation models aligns well with Planck 2018 data, covering most favored regions in the ($n_s$, $r$) parameter space.

Contribution

It introduces a unified phenomenological framework for $ ext{α}$-attractors and Dp-brane inflation models, explaining their predictions in the context of pole inflation.

Findings

Most of the Planck 2018 favored ($n_s$, $r$) region is covered by models with $eta=2$ and $eta=5/3$.

Discrete targets for $r$ are predicted for specific $ ext{α}$-attractor models.

Future $n_s$ measurements could distinguish between these inflationary models.

Abstract

We show that a combination of the simplest $\alpha$-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 $\alpha$-attractor models, there are discrete targets $3\alpha=1,2,...,7$, predicting 7 different values of $r = 12\alpha/N^{2}$ in the range $10^{-2} \gtrsim r \gtrsim 10^{-3}$. In the small $r$ limit, $\alpha$-attractors and Dp-brane inflation models describe vertical $\beta$-stripes in the ($n_{s}$, $r$) space, with $n_{s}=1-\beta/N$, $\beta=2, {5\over 3},{8\over 5}, {3\over 2},{4\over 3}$. A phenomenological description of these models and their generalizations can be achieved in the context of pole inflation. Most of the $1\sigma$ area in the ($n_{s}$, $r$) space favored by Planck 2018 can be covered models with $\beta = 2$ and $\beta = 5/3$. 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.