Automorphisms of punctual Hilbert schemes and symmetric powers of varieties

TL;DR

This paper classifies smooth projective surfaces with non-natural automorphisms of their punctual Hilbert schemes, extending to higher dimensions and characterizing when these schemes determine the variety up to isomorphism.

Contribution

It provides a complete classification of surfaces with non-natural automorphisms of their punctual Hilbert schemes and extends the analysis to higher-dimensional varieties.

Findings

Classified surfaces with non-natural automorphisms of punctual Hilbert schemes.

Established conditions under which symmetric powers have only natural automorphisms.

Characterized surfaces of Kodaira dimension ≥ 1 with non-natural automorphisms.

Abstract

We classify complex smooth projective surfaces whose punctual Hilbert scheme has a non-natural automorphism preserving the big diagonal. This completely answers a question raised by Belmans, Oberdieck and Rennemo, and extends previous works by Boissi{\`e}re-Sarti, Hayashi, Sasaki, Girardet and Wang. We reduce this to studying the existence of non-natural automorphisms of symmetric powers. We study this question for higher dimensional varieties too, giving some sufficient conditions guaranteeing every automorphism of a symmetric power to be natural. As a corollary, we characterize smooth projective surfaces of Kodaira dimension $\geq 1$ whose punctual Hilbert scheme has a non-natural automorphism, this time not assuming the automorphism preserves the big diagonal. We also address the question, when a smooth projective variety is determined up to isomorphism by its punctual Hilbert scheme.