# B-mode Targets

## TL;DR

This paper summarizes recent results on inflationary models predicting B-mode polarization targets for gravitational wave searches, focusing on specific ranges of the tensor-to-scalar ratio and their compatibility with Planck data.

## Contribution

It identifies and analyzes the simplest inflationary models, including $eta$-attractors and D-brane inflation, providing specific B-mode targets for future gravitational wave experiments.

## Key findings

- U-duality symmetric $eta$-attractors define B-mode benchmarks for $10^{-3} \,\lesssim r \lesssim 10^{-2}$.
- Future measurements of $n_s$ will be crucial for models with $r \lesssim 10^{-3}$.
- Combined models cover most of the Planck 2018 favored parameter space.

## Abstract

The CMB-S4 Science Book, Astro2020 Science White Paper on gravitational waves, and PICO report contain an extensive discussion of many ongoing and planned efforts in the search for gravitational waved produced by inflation. Here we give a short executive summary of the results obtained in our recent papers, which specify the simplest available inflationary models providing physically motivated targets for these searches. Our conclusions are specific for the $10^{-3} \lesssim r \lesssim 10^{-2}$ range, where we present the B-mode benchmarks of the U-duality symmetric class of $\alpha$-attractors, and for $ r \lesssim 10^{-3}$, where we present B-mode targets, for which the future precision measurements of $n_s$ will be decisive. We show that a combination of the simplest $\alpha$-attractors and KKLTI models of D-brane inflation covers most of the area favored by Planck 2018.