Unexpected loss of maximality: the case of Hilbert square of real surfaces

Abstract

We explore the maximality of the Hilbert square of maximal real surfaces, and find that in many cases the Hilbert square is maximal if and only if the surface has connected real locus. In particular, the Hilbert square of no maximal K3-surface is maximal. Nevertheless, we exhibit maximal surfaces with disconnected real locus whose Hilbert square is maximal.

Improved presentation. Published in Selecta Mathematica under the title "On the maximality problem for the Hilbert square of real surfaces"