Open Letter to the MILC Collaboration: Why Does the Coarsest Lattice Spacing Stop Just Below the Proton's Compton Wavelength?

The coarsest ensembles used by the MILC collaboration for precision light-hadron physics have had a lattice spacing of about 0.18 fm for more than twenty years, while the finest end of the sequence has moved steadily down (0.15, 0.12, 0.09, 0.06, ≈0.042, 0.03 fm). The proton's reduced Compton wavelength is ƛp = ħ/(mpc) = 0.21031 fm. This letter asks three questions about the position of that upper edge. It makes no claim that lattice QCD results are wrong; it asks for the reasoning behind a limit that, as far as the author could find, is nowhere stated explicitly. Open letter. Background: Appendix A1.4 of Theory of Space, Volume 1. https://theoryof.space