B-mode Targets
  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.
