Stability and deformation of F-singularities

Deformations of log terminal and semi log canonical singularities

In this paper, we prove that klt singularities are invariant under deformations if the generic fiber is $\mathbb{Q}$-Gorenstein. We also obtain a similar result for slc singularities. These are generalizations of results of Esnault-Viehweg and S. Ishii.

Arithmetic and geometric deformations of $F$-pure and $F$-regular singularities

Given a normal $\mathbb{Q}$-Gorenstein complex variety $X$, we prove that if one spreads it out to a normal $\mathbb{Q}$-Gorenstein scheme $\mathcal{X}$ of mixed characteristic whose reduction $\mathcal{X}_p$ modulo $p$ has normal $F$-pure singularities for a single prime $p$, then $X$ has log canonical singularities. In addition, we show its analog for log terminal singularities, without assuming that $\mathcal{X}$ is $\mathbb{Q}$-Gorenstein, which is a generalization of a result of Ma-Schwede. We also prove that two-dimensional strongly $F$-regular singularities are stable under equal charac…

On deformations of maps and curve singularities

We study several deformation functors associated to the normalization of a reduced curve singularity $(X,0) \subset (\c^n,0)$. The main new results are explicit formulas, in terms of classical invariants of (X,0), for the cotangent cohomology groups $T^i, i = 0,1,2,$ of these functors. Thus we obtain precise statements about smoothness and dimension of the corresponding local moduli spaces. We apply the results to obtain explicit formulas resp. estimates for the $\hoa{A}_e$-codimension of a parametrized curve singularity, where $\hoa{A}_e$ denotes the Mather-Wall group of left-right equivalenc…

Tjurina and Milnor numbers of matrix singularities

In order to understand the deformations of determinants and Pfaffians resulting from deformations of matrices, we study the deformation theory of composites $f\circ F$, with isolated singularities, where $f:Y\to\C$ has Cohen-Macaulay singular locus and $F:X\to Y$. We identify the corresponding $T^1(F)$ as (something like) the cohomology of a derived functor, and construct a canonical long exact sequence from which it follows that $$τ=μ(f\circ F)-β_0+β_1,$$ where $τ$ is the length of $T^1(F)$ and $β_i$ is the length of $Tor_i(Ø_Y/J_f,Ø_X)$. This explains numerical coincidences observed in lists…

Gröbner deformation and $F$-singularities

For polynomial ideals in positive charachteristic, defining $F$-split rings and admitting a squarefree monomial initial ideal are different notions. In this note we show that, however, there are strong interactions in both directions. Moreover we provide an overview on which $F$-singularities are Gröbner deforming. Also, we prove the following characteristic-free statement: if $\mathfrak{p}$ is a height $h$ prime ideal such that $\textrm{in}(\mathfrak{p}^{(h)})$ contains at least one squarefree monomial, then $\textrm{in}(\mathfrak{p})$ is a squarefree monomial ideal.

klt奇点的稳定性

Stability of klt singularities

本文综述klt奇点稳定性理论的近期进展，重点围绕稳定退化猜想的求解展开相关研究梳理。