Regularity, singularities and $h$-vector of graded algebras

Abstract

Let $R$ be a standard graded algebra over a field. We investigate how the singularities of $R$ affect its $h$-vector, which is the coefficients of the numerator of its Hilbert series. The most concrete consequences of our work asserts that if $R$ satisfies Serre's condition $(S_r)$ and have reasonable singularities (Du Bois on the punctured spectrum or $F$-pure), then $h_0,\dots ,h_r\ge 0$. Furthermore the multiplicity of $R$ is at least $h_0+h_1+\cdots +h_{r-1}$. We also prove that equality in many cases forces $R$ to be Cohen-Macaulay. The main technical tools are sharp bounds on regularity of certain Ext modules, which can be viewed as Kodaira-type vanishing statements for Du Bois and $F$-singularities. Many corollaries are deduced, for instance that nice singularities of small codimension must be Cohen-Macaulay. Our results build on and extend previous work by de Fernex-Ein, Eisenbud-Goto, Huneke-Smith, Murai-Terai and others.

Final version, to appear in Transactions of the AMS

References in corpus (4)

• The canonical sheaf of Du Bois singularities
• Quasi-log varieties
• Hodge theory meets the minimal model program: a survey of log canonical and Du Bois singularities
• Singularities with respect to Mather-Jacobian discrepancies

Cited by in corpus (2)

• Intrinsic mirror symmetry and categorical crepant resolutions
• Koszul Gorenstein algebras from Cohen-Macaulay simplicial complexes