What produces the gap between super-Earths and sub-Neptunes?

For planets with $P < 100\,\mathrm{d}$ the occurrence rate drops by a factor $\ge 2$ at $R_p \sim 1.5-2.0\,R_{\mathrm{earth}}$, with the gap center decreasing with period roughly as R ~ P^-0.1. Discriminate between XUV photoevaporation (completed in $\sim 10^8\,\mathrm{yr}$), core-powered mass loss ($\sim 10^9\,\mathrm{yr}$), gas-poor late formation, and a water-world population, using the gap dependence on period, stellar mass, age and metallicity.

Gap location and depth versus stellar mass, instellation and age in a large sample with precise radii and masses, compared with the distinct scalings predicted by each mechanism.