The minimal exponent and $k$-rationality for locally complete intersections

Qianyu Chen, Bradley Dirks, Mircea Mustaţă

Published 2022-12-04Version 1

We show that if $Z$ is a locally complete intersection subvariety of a smooth complex variety $X$, of pure codimension $r$, then $Z$ has $k$-rational singularities if and only if $\widetilde{\alpha}(Z)>k+r$, where $\widetilde{\alpha}(Z)$ is the minimal exponent of $Z$. We also characterize this condition in terms of the Hodge filtration on the intersection cohomology Hodge module of $Z$. Furthermore, we show that if $Z$ has $k$-rational singularities, then the Hodge filtration on the local cohomology sheaf $\mathcal{H}^r_Z(\mathcal{O}_X)$ is generated at level $\dim(X)-\lceil \widetilde{\alpha}(Z)\rceil-1$ and, assuming that $k\geq 1$ and $Z$ is singular, of dimension $d$, that $\mathcal{H}^k(\underline{\Omega}_Z^{d-k})\neq 0$. All these results have been known for hypersurfaces in smooth varieties.