Wall-crossing for iterated Hilbert schemes (or ‘Hilb of Hilb’)

We study wall-crossing phenomena in the McKay correspondence. Craw–Ishii show that every projective crepant resolution of a Gorenstein abelian quotient singularity arises as a moduli space of θ-stable representations of the McKay quiver. The stability condition θ moves in a vector space with a chamber decomposition in which (some) wallcrossings capture flops between different crepant resolutions. We investigate where chambers for certain resolutions with Hilbert scheme-like moduli interpretations – iterated Hilbert schemes, or ‘Hilb of Hilb’ – sit relative to the principal chamber defining the usual G-Hilbert scheme. We survey relevant aspects of wall-crossing, pose our main conjecture, prove it for some examples and special cases, and discuss connections to other parts of the McKay correspondence.