On the geometry of punctual Hilbert schemes on singular curves

Abstract: Inspired by the work of Soma and Watari, we define a tree structure on the sub-semimodule of a semi-group $\Gamma$ associated an irreducible curve singularity $(C,O).$ Building on the results of Oblomkov, Rasmussen and Shende, we show that for certain singularities, this tree encodes some aspects of the geometric structure of the punctual Hilbert schemes of $(C,O).$ As an application, we compute the motivic Hilbert zeta function for some singular curves. A point of the Hilbert scheme corresponds to an ideal in the ring of global sections on $(C,O).$ We study the geometry of subsets of these Hilbert schemes defined by constraints on the minimal number of generators of the defining ideal, and describe some of their geometric properties.